UNIVERSIDADE FEDERAL DO CEARÁ CENTRO DE CIÊNCIAS DEPARTAMENTO DE FÍSICA PROGRAMA DE PÓS-GRADUAÇÃO EM FÍSICA MAYRA ALEXANDRA PADRÓN GÓMEZ STRUCTURAL AND OPTICAL PROPERTIES OF LOW DIMENSIONAL LEAD HALIDE PEROVSKITES FORTALEZA-CE 2018
UNIVERSIDADE FEDERAL DO CEARAacute
CENTRO DE CIEcircNCIAS
DEPARTAMENTO DE FIacuteSICA
PROGRAMA DE POacuteS-GRADUACcedilAtildeO EM FIacuteSICA
MAYRA ALEXANDRA PADROacuteN GOacuteMEZ
STRUCTURAL AND OPTICAL PROPERTIES OF LOW
DIMENSIONAL LEAD HALIDE PEROVSKITES
FORTALEZA-CE
2018
2
MAYRA ALEXANDRA PADROacuteN GOacuteMEZ
STRUCTURAL AND OPTICAL PROPERTIES OF LOW DIMENSIONAL
LEAD HALIDE PEROVSKITES
Msc thesis presented to the Post-Graduation
Course in Physics of the Federal University of
Cearaacute as part of the requisites for obtaining the
Degree of Master in Physics
Advisor Prof Dr Alejandro Pedro Ayala
FORTALEZA
2018
3
4
MAYRA ALEXANDRA PADROacuteN GOacuteMEZ
STRUCTURAL AND OPTICAL PROPERTIES OF LOW DIMENSIONAL
LEAD HALIDE PEROVSKITES
Dissertaccedilatildeo de mestrado apresentada ao Programa
de Poacutes-Graduaccedilatildeo em Fiacutesica da Universidade
Federal do Cearaacute como requisito parcial para
obtenccedilatildeo do Tiacutetulo de Mestre em Fiacutesica Aacuterea de
concentraccedilatildeo Fiacutesica da Mateacuteria Condensada
Aprovada em 20082018
BANCA EXAMINADORA
___________________________________________________________
Prof Dr Alejandro Pedro Ayala (Orientador)
Universidade Federal do Cearaacute (UFC)
___________________________________________________________
Prof Dr Carlos William de Arauacutejo Paschoal
Universidade Federal do Cearaacute (UFC)
___________________________________________________________
Prof Dr Maacuterio Ernesto Giroldo Valerio
Universidade Federal de Sergipe (UFS)
5
Acknowledgements
I am very grateful to my advisor Prof Dr Alejandro Pedro Ayala for having accepted me as your
student and having proposed me this project Thank you for your patience dedication and advices
Also for the opportunity to work in your group and learn from you
I like to thank the members of the Jury Prof Dr Carlos William Paschoal and Prof Dr Maacuterio
Ernesto Giroldo Valerio for comments and corrections that made possible this final work My
appreciation also goes to the Prof Dr Alexandre Paschoal and Prof Dr Paulo de Tarso because
with their experience they helped me during the analysis of the techniques involved in this
investigation
Many thanks to Cristiano and Enzo for the help in the measurements of Raman and SNOM
A special acknowledgment to Bruno Wellington e Fabio for the arduous hours we work making
measurements and analysis of Raman and Photoluminescence thank you for your company
I would like to express my appreciation to the members of LabCrEs for their company friendship
and support every day thanks for made the work environment more enjoyable
I very gratitude with the Central Analiacutetica of the UFC for the collaboration in the measurements of
microscopy and EDX
I would like to thank my family for all the support To my parents my brothers my uncles my
cousins my parents in law and friends Despite the distance they have always supported me
Thanks Juan for always be there and be my partner friend boyfriend colleague and believe in me
in the days that I did not Thank you for being the person who makes happy my days and
accompany me in this goal that we proposed to reach together I love you
Thanks to the UFC and Pos-Graduation for give me the opportunity of study Finally I would like
to thanks CAPES for the financial support
6
Abstract
The study of perovskites in last few years has grown exponentially and made then one of the
trending topic in materials science The lead-based family of perovskites are important for their
multiple applications as strong photoluminescence narrow emission line width and high exciton
binding energy Hybrid organic-inorganic perovskites are being widely explored for their
optoelectronic properties few of these materials exhibit broadband emission under ultraviolet
excitation In this work we were synthesized using the slow evaporation method five single
crystals of lead halide perovskites three of them are low dimensional hybrid lead perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 all compounds exhibit a novel crystal
structure Additionally we discuss the behavior of CsPb2Br43I07 and Cs4PbBr6 also low
dimensional compounds under high pressure investigated using Raman and photoluminescence
techniques Several structural phase transitions were identified on this compounds
Keywords Halide perovskites crystallography Raman spectroscopy hydrostatic pressure
7
Resumo
O estudo das perovskitas nos uacuteltimos anos cresceu exponencialmente e tornou-se um dos temas
dominantes na ciecircncia dos materiais A famiacutelia de perovskitas baseadas em chumbo eacute importante
pelas suas muacuteltiplas aplicaccedilotildees como forte fotoluminescecircncia estreita largura de linha de emissatildeo
e alta energia de ligaccedilatildeo de excitons Perovskitas hiacutebridas orgacircnicas e inorgacircnicas estatildeo sendo
amplamente exploradas por suas propriedades optoeletrocircnicas alguns destes materiais exibem uma
banda de emissatildeo larga quando excita no ultravioleta Neste trabalho foram sintetizados utilizando
o meacutetodo de evaporaccedilatildeo lenta cinco monocristais de perovskitas de haleto de chumbo sendo trecircs
perovskitas hiacutebridas de baixa dimensionalidade (DMA)11Pb4Br19 (DMA)14RbPb4Br23 e
(DMA)9S4Pb5Br27 todos os compostos exibem novas estruturas cristalinas Adicionalmente
discutimos o comportamento de CsPb2Br43I07 e Cs4PbBr6 tambeacutem compostos de baixa
dimensionalidade investigados a alta pressatildeo usando as teacutecnicas de Raman e fotoluminescecircncia
Vaacuterias transiccedilotildees de fase estruturais foram identificadas nestes compostos
Palavras-chave Perovskitas de haleto cristalografia Espectroscopia Raman pressatildeo
hidrostaacutetica
8
List of Figures
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green spheres
halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres oxygen atoms
purple polyhedrons metal halide octahedra hydrogen atoms are hidden for clarity) as well as their
corresponding conventional materials with different dimensionalities 2D 1D and 0D perovskites can
therefore be considered as bulk assemblies of 2D quantum wells 1D quantum wires and 0D
moleculesclusters12 13
Figure 2 Single crystal diffractometer Bruker D8 VENTURE 23
Figure 3 LabRam HR 800 HORIBA 25
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450 26
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 28
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a b and c
axis and (b) 2x1x2 bounding octahedrons 29
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 30
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and each
element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19 perovskite
34
Figure 9 CsPb2(Br085I015)5 unit cell 36
Figure 10 CsPb2Br426I074 single crystal EDX Images 37
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure 38
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent phonon
positions 39
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center 41
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room temperature and
pressure The red continuous line represents the result of the decomposition of the spectrum with a set of
Lorentzian line profiles (blue lines) which are also shown in the figure 44
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high pressure
conditions up to 1085 GPa Several pressure-induced phase transitions are observed (b)Wavenumber vs
pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for compression experiments The
vertical lines indicate the pressures at which Cs4PbBr6 undergoes phase transitions 46
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission center
and intensity 47
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
2
MAYRA ALEXANDRA PADROacuteN GOacuteMEZ
STRUCTURAL AND OPTICAL PROPERTIES OF LOW DIMENSIONAL
LEAD HALIDE PEROVSKITES
Msc thesis presented to the Post-Graduation
Course in Physics of the Federal University of
Cearaacute as part of the requisites for obtaining the
Degree of Master in Physics
Advisor Prof Dr Alejandro Pedro Ayala
FORTALEZA
2018
3
4
MAYRA ALEXANDRA PADROacuteN GOacuteMEZ
STRUCTURAL AND OPTICAL PROPERTIES OF LOW DIMENSIONAL
LEAD HALIDE PEROVSKITES
Dissertaccedilatildeo de mestrado apresentada ao Programa
de Poacutes-Graduaccedilatildeo em Fiacutesica da Universidade
Federal do Cearaacute como requisito parcial para
obtenccedilatildeo do Tiacutetulo de Mestre em Fiacutesica Aacuterea de
concentraccedilatildeo Fiacutesica da Mateacuteria Condensada
Aprovada em 20082018
BANCA EXAMINADORA
___________________________________________________________
Prof Dr Alejandro Pedro Ayala (Orientador)
Universidade Federal do Cearaacute (UFC)
___________________________________________________________
Prof Dr Carlos William de Arauacutejo Paschoal
Universidade Federal do Cearaacute (UFC)
___________________________________________________________
Prof Dr Maacuterio Ernesto Giroldo Valerio
Universidade Federal de Sergipe (UFS)
5
Acknowledgements
I am very grateful to my advisor Prof Dr Alejandro Pedro Ayala for having accepted me as your
student and having proposed me this project Thank you for your patience dedication and advices
Also for the opportunity to work in your group and learn from you
I like to thank the members of the Jury Prof Dr Carlos William Paschoal and Prof Dr Maacuterio
Ernesto Giroldo Valerio for comments and corrections that made possible this final work My
appreciation also goes to the Prof Dr Alexandre Paschoal and Prof Dr Paulo de Tarso because
with their experience they helped me during the analysis of the techniques involved in this
investigation
Many thanks to Cristiano and Enzo for the help in the measurements of Raman and SNOM
A special acknowledgment to Bruno Wellington e Fabio for the arduous hours we work making
measurements and analysis of Raman and Photoluminescence thank you for your company
I would like to express my appreciation to the members of LabCrEs for their company friendship
and support every day thanks for made the work environment more enjoyable
I very gratitude with the Central Analiacutetica of the UFC for the collaboration in the measurements of
microscopy and EDX
I would like to thank my family for all the support To my parents my brothers my uncles my
cousins my parents in law and friends Despite the distance they have always supported me
Thanks Juan for always be there and be my partner friend boyfriend colleague and believe in me
in the days that I did not Thank you for being the person who makes happy my days and
accompany me in this goal that we proposed to reach together I love you
Thanks to the UFC and Pos-Graduation for give me the opportunity of study Finally I would like
to thanks CAPES for the financial support
6
Abstract
The study of perovskites in last few years has grown exponentially and made then one of the
trending topic in materials science The lead-based family of perovskites are important for their
multiple applications as strong photoluminescence narrow emission line width and high exciton
binding energy Hybrid organic-inorganic perovskites are being widely explored for their
optoelectronic properties few of these materials exhibit broadband emission under ultraviolet
excitation In this work we were synthesized using the slow evaporation method five single
crystals of lead halide perovskites three of them are low dimensional hybrid lead perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 all compounds exhibit a novel crystal
structure Additionally we discuss the behavior of CsPb2Br43I07 and Cs4PbBr6 also low
dimensional compounds under high pressure investigated using Raman and photoluminescence
techniques Several structural phase transitions were identified on this compounds
Keywords Halide perovskites crystallography Raman spectroscopy hydrostatic pressure
7
Resumo
O estudo das perovskitas nos uacuteltimos anos cresceu exponencialmente e tornou-se um dos temas
dominantes na ciecircncia dos materiais A famiacutelia de perovskitas baseadas em chumbo eacute importante
pelas suas muacuteltiplas aplicaccedilotildees como forte fotoluminescecircncia estreita largura de linha de emissatildeo
e alta energia de ligaccedilatildeo de excitons Perovskitas hiacutebridas orgacircnicas e inorgacircnicas estatildeo sendo
amplamente exploradas por suas propriedades optoeletrocircnicas alguns destes materiais exibem uma
banda de emissatildeo larga quando excita no ultravioleta Neste trabalho foram sintetizados utilizando
o meacutetodo de evaporaccedilatildeo lenta cinco monocristais de perovskitas de haleto de chumbo sendo trecircs
perovskitas hiacutebridas de baixa dimensionalidade (DMA)11Pb4Br19 (DMA)14RbPb4Br23 e
(DMA)9S4Pb5Br27 todos os compostos exibem novas estruturas cristalinas Adicionalmente
discutimos o comportamento de CsPb2Br43I07 e Cs4PbBr6 tambeacutem compostos de baixa
dimensionalidade investigados a alta pressatildeo usando as teacutecnicas de Raman e fotoluminescecircncia
Vaacuterias transiccedilotildees de fase estruturais foram identificadas nestes compostos
Palavras-chave Perovskitas de haleto cristalografia Espectroscopia Raman pressatildeo
hidrostaacutetica
8
List of Figures
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green spheres
halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres oxygen atoms
purple polyhedrons metal halide octahedra hydrogen atoms are hidden for clarity) as well as their
corresponding conventional materials with different dimensionalities 2D 1D and 0D perovskites can
therefore be considered as bulk assemblies of 2D quantum wells 1D quantum wires and 0D
moleculesclusters12 13
Figure 2 Single crystal diffractometer Bruker D8 VENTURE 23
Figure 3 LabRam HR 800 HORIBA 25
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450 26
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 28
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a b and c
axis and (b) 2x1x2 bounding octahedrons 29
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 30
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and each
element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19 perovskite
34
Figure 9 CsPb2(Br085I015)5 unit cell 36
Figure 10 CsPb2Br426I074 single crystal EDX Images 37
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure 38
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent phonon
positions 39
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center 41
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room temperature and
pressure The red continuous line represents the result of the decomposition of the spectrum with a set of
Lorentzian line profiles (blue lines) which are also shown in the figure 44
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high pressure
conditions up to 1085 GPa Several pressure-induced phase transitions are observed (b)Wavenumber vs
pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for compression experiments The
vertical lines indicate the pressures at which Cs4PbBr6 undergoes phase transitions 46
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission center
and intensity 47
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
3
4
MAYRA ALEXANDRA PADROacuteN GOacuteMEZ
STRUCTURAL AND OPTICAL PROPERTIES OF LOW DIMENSIONAL
LEAD HALIDE PEROVSKITES
Dissertaccedilatildeo de mestrado apresentada ao Programa
de Poacutes-Graduaccedilatildeo em Fiacutesica da Universidade
Federal do Cearaacute como requisito parcial para
obtenccedilatildeo do Tiacutetulo de Mestre em Fiacutesica Aacuterea de
concentraccedilatildeo Fiacutesica da Mateacuteria Condensada
Aprovada em 20082018
BANCA EXAMINADORA
___________________________________________________________
Prof Dr Alejandro Pedro Ayala (Orientador)
Universidade Federal do Cearaacute (UFC)
___________________________________________________________
Prof Dr Carlos William de Arauacutejo Paschoal
Universidade Federal do Cearaacute (UFC)
___________________________________________________________
Prof Dr Maacuterio Ernesto Giroldo Valerio
Universidade Federal de Sergipe (UFS)
5
Acknowledgements
I am very grateful to my advisor Prof Dr Alejandro Pedro Ayala for having accepted me as your
student and having proposed me this project Thank you for your patience dedication and advices
Also for the opportunity to work in your group and learn from you
I like to thank the members of the Jury Prof Dr Carlos William Paschoal and Prof Dr Maacuterio
Ernesto Giroldo Valerio for comments and corrections that made possible this final work My
appreciation also goes to the Prof Dr Alexandre Paschoal and Prof Dr Paulo de Tarso because
with their experience they helped me during the analysis of the techniques involved in this
investigation
Many thanks to Cristiano and Enzo for the help in the measurements of Raman and SNOM
A special acknowledgment to Bruno Wellington e Fabio for the arduous hours we work making
measurements and analysis of Raman and Photoluminescence thank you for your company
I would like to express my appreciation to the members of LabCrEs for their company friendship
and support every day thanks for made the work environment more enjoyable
I very gratitude with the Central Analiacutetica of the UFC for the collaboration in the measurements of
microscopy and EDX
I would like to thank my family for all the support To my parents my brothers my uncles my
cousins my parents in law and friends Despite the distance they have always supported me
Thanks Juan for always be there and be my partner friend boyfriend colleague and believe in me
in the days that I did not Thank you for being the person who makes happy my days and
accompany me in this goal that we proposed to reach together I love you
Thanks to the UFC and Pos-Graduation for give me the opportunity of study Finally I would like
to thanks CAPES for the financial support
6
Abstract
The study of perovskites in last few years has grown exponentially and made then one of the
trending topic in materials science The lead-based family of perovskites are important for their
multiple applications as strong photoluminescence narrow emission line width and high exciton
binding energy Hybrid organic-inorganic perovskites are being widely explored for their
optoelectronic properties few of these materials exhibit broadband emission under ultraviolet
excitation In this work we were synthesized using the slow evaporation method five single
crystals of lead halide perovskites three of them are low dimensional hybrid lead perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 all compounds exhibit a novel crystal
structure Additionally we discuss the behavior of CsPb2Br43I07 and Cs4PbBr6 also low
dimensional compounds under high pressure investigated using Raman and photoluminescence
techniques Several structural phase transitions were identified on this compounds
Keywords Halide perovskites crystallography Raman spectroscopy hydrostatic pressure
7
Resumo
O estudo das perovskitas nos uacuteltimos anos cresceu exponencialmente e tornou-se um dos temas
dominantes na ciecircncia dos materiais A famiacutelia de perovskitas baseadas em chumbo eacute importante
pelas suas muacuteltiplas aplicaccedilotildees como forte fotoluminescecircncia estreita largura de linha de emissatildeo
e alta energia de ligaccedilatildeo de excitons Perovskitas hiacutebridas orgacircnicas e inorgacircnicas estatildeo sendo
amplamente exploradas por suas propriedades optoeletrocircnicas alguns destes materiais exibem uma
banda de emissatildeo larga quando excita no ultravioleta Neste trabalho foram sintetizados utilizando
o meacutetodo de evaporaccedilatildeo lenta cinco monocristais de perovskitas de haleto de chumbo sendo trecircs
perovskitas hiacutebridas de baixa dimensionalidade (DMA)11Pb4Br19 (DMA)14RbPb4Br23 e
(DMA)9S4Pb5Br27 todos os compostos exibem novas estruturas cristalinas Adicionalmente
discutimos o comportamento de CsPb2Br43I07 e Cs4PbBr6 tambeacutem compostos de baixa
dimensionalidade investigados a alta pressatildeo usando as teacutecnicas de Raman e fotoluminescecircncia
Vaacuterias transiccedilotildees de fase estruturais foram identificadas nestes compostos
Palavras-chave Perovskitas de haleto cristalografia Espectroscopia Raman pressatildeo
hidrostaacutetica
8
List of Figures
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green spheres
halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres oxygen atoms
purple polyhedrons metal halide octahedra hydrogen atoms are hidden for clarity) as well as their
corresponding conventional materials with different dimensionalities 2D 1D and 0D perovskites can
therefore be considered as bulk assemblies of 2D quantum wells 1D quantum wires and 0D
moleculesclusters12 13
Figure 2 Single crystal diffractometer Bruker D8 VENTURE 23
Figure 3 LabRam HR 800 HORIBA 25
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450 26
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 28
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a b and c
axis and (b) 2x1x2 bounding octahedrons 29
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 30
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and each
element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19 perovskite
34
Figure 9 CsPb2(Br085I015)5 unit cell 36
Figure 10 CsPb2Br426I074 single crystal EDX Images 37
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure 38
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent phonon
positions 39
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center 41
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room temperature and
pressure The red continuous line represents the result of the decomposition of the spectrum with a set of
Lorentzian line profiles (blue lines) which are also shown in the figure 44
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high pressure
conditions up to 1085 GPa Several pressure-induced phase transitions are observed (b)Wavenumber vs
pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for compression experiments The
vertical lines indicate the pressures at which Cs4PbBr6 undergoes phase transitions 46
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission center
and intensity 47
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
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BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
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CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
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CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
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CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
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2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
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DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
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DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
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DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
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53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
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Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
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HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
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HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
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HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
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HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
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HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
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JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
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p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
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KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
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KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
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Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
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LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
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LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
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LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
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LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
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SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
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SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
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(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
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SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
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TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
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TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
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VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
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WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
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WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
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YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
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YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
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ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
4
MAYRA ALEXANDRA PADROacuteN GOacuteMEZ
STRUCTURAL AND OPTICAL PROPERTIES OF LOW DIMENSIONAL
LEAD HALIDE PEROVSKITES
Dissertaccedilatildeo de mestrado apresentada ao Programa
de Poacutes-Graduaccedilatildeo em Fiacutesica da Universidade
Federal do Cearaacute como requisito parcial para
obtenccedilatildeo do Tiacutetulo de Mestre em Fiacutesica Aacuterea de
concentraccedilatildeo Fiacutesica da Mateacuteria Condensada
Aprovada em 20082018
BANCA EXAMINADORA
___________________________________________________________
Prof Dr Alejandro Pedro Ayala (Orientador)
Universidade Federal do Cearaacute (UFC)
___________________________________________________________
Prof Dr Carlos William de Arauacutejo Paschoal
Universidade Federal do Cearaacute (UFC)
___________________________________________________________
Prof Dr Maacuterio Ernesto Giroldo Valerio
Universidade Federal de Sergipe (UFS)
5
Acknowledgements
I am very grateful to my advisor Prof Dr Alejandro Pedro Ayala for having accepted me as your
student and having proposed me this project Thank you for your patience dedication and advices
Also for the opportunity to work in your group and learn from you
I like to thank the members of the Jury Prof Dr Carlos William Paschoal and Prof Dr Maacuterio
Ernesto Giroldo Valerio for comments and corrections that made possible this final work My
appreciation also goes to the Prof Dr Alexandre Paschoal and Prof Dr Paulo de Tarso because
with their experience they helped me during the analysis of the techniques involved in this
investigation
Many thanks to Cristiano and Enzo for the help in the measurements of Raman and SNOM
A special acknowledgment to Bruno Wellington e Fabio for the arduous hours we work making
measurements and analysis of Raman and Photoluminescence thank you for your company
I would like to express my appreciation to the members of LabCrEs for their company friendship
and support every day thanks for made the work environment more enjoyable
I very gratitude with the Central Analiacutetica of the UFC for the collaboration in the measurements of
microscopy and EDX
I would like to thank my family for all the support To my parents my brothers my uncles my
cousins my parents in law and friends Despite the distance they have always supported me
Thanks Juan for always be there and be my partner friend boyfriend colleague and believe in me
in the days that I did not Thank you for being the person who makes happy my days and
accompany me in this goal that we proposed to reach together I love you
Thanks to the UFC and Pos-Graduation for give me the opportunity of study Finally I would like
to thanks CAPES for the financial support
6
Abstract
The study of perovskites in last few years has grown exponentially and made then one of the
trending topic in materials science The lead-based family of perovskites are important for their
multiple applications as strong photoluminescence narrow emission line width and high exciton
binding energy Hybrid organic-inorganic perovskites are being widely explored for their
optoelectronic properties few of these materials exhibit broadband emission under ultraviolet
excitation In this work we were synthesized using the slow evaporation method five single
crystals of lead halide perovskites three of them are low dimensional hybrid lead perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 all compounds exhibit a novel crystal
structure Additionally we discuss the behavior of CsPb2Br43I07 and Cs4PbBr6 also low
dimensional compounds under high pressure investigated using Raman and photoluminescence
techniques Several structural phase transitions were identified on this compounds
Keywords Halide perovskites crystallography Raman spectroscopy hydrostatic pressure
7
Resumo
O estudo das perovskitas nos uacuteltimos anos cresceu exponencialmente e tornou-se um dos temas
dominantes na ciecircncia dos materiais A famiacutelia de perovskitas baseadas em chumbo eacute importante
pelas suas muacuteltiplas aplicaccedilotildees como forte fotoluminescecircncia estreita largura de linha de emissatildeo
e alta energia de ligaccedilatildeo de excitons Perovskitas hiacutebridas orgacircnicas e inorgacircnicas estatildeo sendo
amplamente exploradas por suas propriedades optoeletrocircnicas alguns destes materiais exibem uma
banda de emissatildeo larga quando excita no ultravioleta Neste trabalho foram sintetizados utilizando
o meacutetodo de evaporaccedilatildeo lenta cinco monocristais de perovskitas de haleto de chumbo sendo trecircs
perovskitas hiacutebridas de baixa dimensionalidade (DMA)11Pb4Br19 (DMA)14RbPb4Br23 e
(DMA)9S4Pb5Br27 todos os compostos exibem novas estruturas cristalinas Adicionalmente
discutimos o comportamento de CsPb2Br43I07 e Cs4PbBr6 tambeacutem compostos de baixa
dimensionalidade investigados a alta pressatildeo usando as teacutecnicas de Raman e fotoluminescecircncia
Vaacuterias transiccedilotildees de fase estruturais foram identificadas nestes compostos
Palavras-chave Perovskitas de haleto cristalografia Espectroscopia Raman pressatildeo
hidrostaacutetica
8
List of Figures
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green spheres
halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres oxygen atoms
purple polyhedrons metal halide octahedra hydrogen atoms are hidden for clarity) as well as their
corresponding conventional materials with different dimensionalities 2D 1D and 0D perovskites can
therefore be considered as bulk assemblies of 2D quantum wells 1D quantum wires and 0D
moleculesclusters12 13
Figure 2 Single crystal diffractometer Bruker D8 VENTURE 23
Figure 3 LabRam HR 800 HORIBA 25
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450 26
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 28
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a b and c
axis and (b) 2x1x2 bounding octahedrons 29
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 30
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and each
element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19 perovskite
34
Figure 9 CsPb2(Br085I015)5 unit cell 36
Figure 10 CsPb2Br426I074 single crystal EDX Images 37
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure 38
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent phonon
positions 39
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center 41
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room temperature and
pressure The red continuous line represents the result of the decomposition of the spectrum with a set of
Lorentzian line profiles (blue lines) which are also shown in the figure 44
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high pressure
conditions up to 1085 GPa Several pressure-induced phase transitions are observed (b)Wavenumber vs
pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for compression experiments The
vertical lines indicate the pressures at which Cs4PbBr6 undergoes phase transitions 46
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission center
and intensity 47
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
5
Acknowledgements
I am very grateful to my advisor Prof Dr Alejandro Pedro Ayala for having accepted me as your
student and having proposed me this project Thank you for your patience dedication and advices
Also for the opportunity to work in your group and learn from you
I like to thank the members of the Jury Prof Dr Carlos William Paschoal and Prof Dr Maacuterio
Ernesto Giroldo Valerio for comments and corrections that made possible this final work My
appreciation also goes to the Prof Dr Alexandre Paschoal and Prof Dr Paulo de Tarso because
with their experience they helped me during the analysis of the techniques involved in this
investigation
Many thanks to Cristiano and Enzo for the help in the measurements of Raman and SNOM
A special acknowledgment to Bruno Wellington e Fabio for the arduous hours we work making
measurements and analysis of Raman and Photoluminescence thank you for your company
I would like to express my appreciation to the members of LabCrEs for their company friendship
and support every day thanks for made the work environment more enjoyable
I very gratitude with the Central Analiacutetica of the UFC for the collaboration in the measurements of
microscopy and EDX
I would like to thank my family for all the support To my parents my brothers my uncles my
cousins my parents in law and friends Despite the distance they have always supported me
Thanks Juan for always be there and be my partner friend boyfriend colleague and believe in me
in the days that I did not Thank you for being the person who makes happy my days and
accompany me in this goal that we proposed to reach together I love you
Thanks to the UFC and Pos-Graduation for give me the opportunity of study Finally I would like
to thanks CAPES for the financial support
6
Abstract
The study of perovskites in last few years has grown exponentially and made then one of the
trending topic in materials science The lead-based family of perovskites are important for their
multiple applications as strong photoluminescence narrow emission line width and high exciton
binding energy Hybrid organic-inorganic perovskites are being widely explored for their
optoelectronic properties few of these materials exhibit broadband emission under ultraviolet
excitation In this work we were synthesized using the slow evaporation method five single
crystals of lead halide perovskites three of them are low dimensional hybrid lead perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 all compounds exhibit a novel crystal
structure Additionally we discuss the behavior of CsPb2Br43I07 and Cs4PbBr6 also low
dimensional compounds under high pressure investigated using Raman and photoluminescence
techniques Several structural phase transitions were identified on this compounds
Keywords Halide perovskites crystallography Raman spectroscopy hydrostatic pressure
7
Resumo
O estudo das perovskitas nos uacuteltimos anos cresceu exponencialmente e tornou-se um dos temas
dominantes na ciecircncia dos materiais A famiacutelia de perovskitas baseadas em chumbo eacute importante
pelas suas muacuteltiplas aplicaccedilotildees como forte fotoluminescecircncia estreita largura de linha de emissatildeo
e alta energia de ligaccedilatildeo de excitons Perovskitas hiacutebridas orgacircnicas e inorgacircnicas estatildeo sendo
amplamente exploradas por suas propriedades optoeletrocircnicas alguns destes materiais exibem uma
banda de emissatildeo larga quando excita no ultravioleta Neste trabalho foram sintetizados utilizando
o meacutetodo de evaporaccedilatildeo lenta cinco monocristais de perovskitas de haleto de chumbo sendo trecircs
perovskitas hiacutebridas de baixa dimensionalidade (DMA)11Pb4Br19 (DMA)14RbPb4Br23 e
(DMA)9S4Pb5Br27 todos os compostos exibem novas estruturas cristalinas Adicionalmente
discutimos o comportamento de CsPb2Br43I07 e Cs4PbBr6 tambeacutem compostos de baixa
dimensionalidade investigados a alta pressatildeo usando as teacutecnicas de Raman e fotoluminescecircncia
Vaacuterias transiccedilotildees de fase estruturais foram identificadas nestes compostos
Palavras-chave Perovskitas de haleto cristalografia Espectroscopia Raman pressatildeo
hidrostaacutetica
8
List of Figures
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green spheres
halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres oxygen atoms
purple polyhedrons metal halide octahedra hydrogen atoms are hidden for clarity) as well as their
corresponding conventional materials with different dimensionalities 2D 1D and 0D perovskites can
therefore be considered as bulk assemblies of 2D quantum wells 1D quantum wires and 0D
moleculesclusters12 13
Figure 2 Single crystal diffractometer Bruker D8 VENTURE 23
Figure 3 LabRam HR 800 HORIBA 25
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450 26
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 28
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a b and c
axis and (b) 2x1x2 bounding octahedrons 29
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 30
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and each
element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19 perovskite
34
Figure 9 CsPb2(Br085I015)5 unit cell 36
Figure 10 CsPb2Br426I074 single crystal EDX Images 37
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure 38
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent phonon
positions 39
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center 41
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room temperature and
pressure The red continuous line represents the result of the decomposition of the spectrum with a set of
Lorentzian line profiles (blue lines) which are also shown in the figure 44
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high pressure
conditions up to 1085 GPa Several pressure-induced phase transitions are observed (b)Wavenumber vs
pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for compression experiments The
vertical lines indicate the pressures at which Cs4PbBr6 undergoes phase transitions 46
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission center
and intensity 47
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
6
Abstract
The study of perovskites in last few years has grown exponentially and made then one of the
trending topic in materials science The lead-based family of perovskites are important for their
multiple applications as strong photoluminescence narrow emission line width and high exciton
binding energy Hybrid organic-inorganic perovskites are being widely explored for their
optoelectronic properties few of these materials exhibit broadband emission under ultraviolet
excitation In this work we were synthesized using the slow evaporation method five single
crystals of lead halide perovskites three of them are low dimensional hybrid lead perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 all compounds exhibit a novel crystal
structure Additionally we discuss the behavior of CsPb2Br43I07 and Cs4PbBr6 also low
dimensional compounds under high pressure investigated using Raman and photoluminescence
techniques Several structural phase transitions were identified on this compounds
Keywords Halide perovskites crystallography Raman spectroscopy hydrostatic pressure
7
Resumo
O estudo das perovskitas nos uacuteltimos anos cresceu exponencialmente e tornou-se um dos temas
dominantes na ciecircncia dos materiais A famiacutelia de perovskitas baseadas em chumbo eacute importante
pelas suas muacuteltiplas aplicaccedilotildees como forte fotoluminescecircncia estreita largura de linha de emissatildeo
e alta energia de ligaccedilatildeo de excitons Perovskitas hiacutebridas orgacircnicas e inorgacircnicas estatildeo sendo
amplamente exploradas por suas propriedades optoeletrocircnicas alguns destes materiais exibem uma
banda de emissatildeo larga quando excita no ultravioleta Neste trabalho foram sintetizados utilizando
o meacutetodo de evaporaccedilatildeo lenta cinco monocristais de perovskitas de haleto de chumbo sendo trecircs
perovskitas hiacutebridas de baixa dimensionalidade (DMA)11Pb4Br19 (DMA)14RbPb4Br23 e
(DMA)9S4Pb5Br27 todos os compostos exibem novas estruturas cristalinas Adicionalmente
discutimos o comportamento de CsPb2Br43I07 e Cs4PbBr6 tambeacutem compostos de baixa
dimensionalidade investigados a alta pressatildeo usando as teacutecnicas de Raman e fotoluminescecircncia
Vaacuterias transiccedilotildees de fase estruturais foram identificadas nestes compostos
Palavras-chave Perovskitas de haleto cristalografia Espectroscopia Raman pressatildeo
hidrostaacutetica
8
List of Figures
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green spheres
halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres oxygen atoms
purple polyhedrons metal halide octahedra hydrogen atoms are hidden for clarity) as well as their
corresponding conventional materials with different dimensionalities 2D 1D and 0D perovskites can
therefore be considered as bulk assemblies of 2D quantum wells 1D quantum wires and 0D
moleculesclusters12 13
Figure 2 Single crystal diffractometer Bruker D8 VENTURE 23
Figure 3 LabRam HR 800 HORIBA 25
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450 26
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 28
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a b and c
axis and (b) 2x1x2 bounding octahedrons 29
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 30
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and each
element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19 perovskite
34
Figure 9 CsPb2(Br085I015)5 unit cell 36
Figure 10 CsPb2Br426I074 single crystal EDX Images 37
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure 38
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent phonon
positions 39
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center 41
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room temperature and
pressure The red continuous line represents the result of the decomposition of the spectrum with a set of
Lorentzian line profiles (blue lines) which are also shown in the figure 44
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high pressure
conditions up to 1085 GPa Several pressure-induced phase transitions are observed (b)Wavenumber vs
pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for compression experiments The
vertical lines indicate the pressures at which Cs4PbBr6 undergoes phase transitions 46
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission center
and intensity 47
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
7
Resumo
O estudo das perovskitas nos uacuteltimos anos cresceu exponencialmente e tornou-se um dos temas
dominantes na ciecircncia dos materiais A famiacutelia de perovskitas baseadas em chumbo eacute importante
pelas suas muacuteltiplas aplicaccedilotildees como forte fotoluminescecircncia estreita largura de linha de emissatildeo
e alta energia de ligaccedilatildeo de excitons Perovskitas hiacutebridas orgacircnicas e inorgacircnicas estatildeo sendo
amplamente exploradas por suas propriedades optoeletrocircnicas alguns destes materiais exibem uma
banda de emissatildeo larga quando excita no ultravioleta Neste trabalho foram sintetizados utilizando
o meacutetodo de evaporaccedilatildeo lenta cinco monocristais de perovskitas de haleto de chumbo sendo trecircs
perovskitas hiacutebridas de baixa dimensionalidade (DMA)11Pb4Br19 (DMA)14RbPb4Br23 e
(DMA)9S4Pb5Br27 todos os compostos exibem novas estruturas cristalinas Adicionalmente
discutimos o comportamento de CsPb2Br43I07 e Cs4PbBr6 tambeacutem compostos de baixa
dimensionalidade investigados a alta pressatildeo usando as teacutecnicas de Raman e fotoluminescecircncia
Vaacuterias transiccedilotildees de fase estruturais foram identificadas nestes compostos
Palavras-chave Perovskitas de haleto cristalografia Espectroscopia Raman pressatildeo
hidrostaacutetica
8
List of Figures
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green spheres
halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres oxygen atoms
purple polyhedrons metal halide octahedra hydrogen atoms are hidden for clarity) as well as their
corresponding conventional materials with different dimensionalities 2D 1D and 0D perovskites can
therefore be considered as bulk assemblies of 2D quantum wells 1D quantum wires and 0D
moleculesclusters12 13
Figure 2 Single crystal diffractometer Bruker D8 VENTURE 23
Figure 3 LabRam HR 800 HORIBA 25
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450 26
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 28
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a b and c
axis and (b) 2x1x2 bounding octahedrons 29
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 30
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and each
element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19 perovskite
34
Figure 9 CsPb2(Br085I015)5 unit cell 36
Figure 10 CsPb2Br426I074 single crystal EDX Images 37
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure 38
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent phonon
positions 39
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center 41
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room temperature and
pressure The red continuous line represents the result of the decomposition of the spectrum with a set of
Lorentzian line profiles (blue lines) which are also shown in the figure 44
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high pressure
conditions up to 1085 GPa Several pressure-induced phase transitions are observed (b)Wavenumber vs
pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for compression experiments The
vertical lines indicate the pressures at which Cs4PbBr6 undergoes phase transitions 46
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission center
and intensity 47
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
8
List of Figures
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green spheres
halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres oxygen atoms
purple polyhedrons metal halide octahedra hydrogen atoms are hidden for clarity) as well as their
corresponding conventional materials with different dimensionalities 2D 1D and 0D perovskites can
therefore be considered as bulk assemblies of 2D quantum wells 1D quantum wires and 0D
moleculesclusters12 13
Figure 2 Single crystal diffractometer Bruker D8 VENTURE 23
Figure 3 LabRam HR 800 HORIBA 25
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450 26
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 28
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a b and c
axis and (b) 2x1x2 bounding octahedrons 29
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the a b and c
axis and (b) 1x2x2 bounding octahedrons 30
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and each
element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19 perovskite
34
Figure 9 CsPb2(Br085I015)5 unit cell 36
Figure 10 CsPb2Br426I074 single crystal EDX Images 37
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure 38
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent phonon
positions 39
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center 41
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room temperature and
pressure The red continuous line represents the result of the decomposition of the spectrum with a set of
Lorentzian line profiles (blue lines) which are also shown in the figure 44
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high pressure
conditions up to 1085 GPa Several pressure-induced phase transitions are observed (b)Wavenumber vs
pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for compression experiments The
vertical lines indicate the pressures at which Cs4PbBr6 undergoes phase transitions 46
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission center
and intensity 47
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
9
List of tables
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t) 15
Table 2Effective Radii of Molecular Cations and Anions 17 16
Table 3 Reported crystal parameters for each novel hybrid perovskites 32
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal CsPb2(Br085I015)5
38
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal 42
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site species γ is
given by the symbol 119891120574 The translational and rotational degrees of freedom of the (PbBr6)4minus octahedra
become translational and vibrational lattice modes in the crystal 43
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
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BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
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FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
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HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
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LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
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SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
10
List of abbreviations
XRD X-ray diffraction
SEM Scanning electron microscopy
PL Photoluminescence
EDX Energy-dispersive X-ray spectroscopy
PCE Power conversion efficiency
DMA Dimethylammonium
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
11
Contents
Introduction 12
Cesium-Lead-Halide Perovskites 17
Chapter 1 20
Experimental Section 20
Materials 20
Synthesis procedures 20
Cs4PbBr6 20
CsPb2Br5I 21
(DMA)11Pb4Br19 21
(DMA)14RbPb4Br23 21
(DMA)9S4Pb5Br27 21
Single-crystal X-ray diffraction 22
Raman spectroscopy 24
Scanning Electron Microscopy (SEM) 25
Chapter 2 27
New Family of Lead Hybrid Perovskites 27
Chapter 3 35
CsPb2Br5I under High-pressure 35
Chapter 4 42
Pressure-Induced enhanced photoluminescence and Raman scattering study of the zero
dimensional Cs4PbBr6 lead halide perovskite 42
Conclusions 49
References 52
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
12
Introduction
In recent years perovskites emerged as a highly promising solution as materials for last
generation applications(YIN et al 2017a) There has been a large interest from technological point
of view because perovskites exhibit distinctive electric magnetic and optical properties(TILLEY
2016) These compounds have emerged as promising materials in diverse fields such as
optoelectronic devices photovoltaic devices and photodetectors According to data extracted from
Web of Science the number of publications in the last few years has grown exponentially which
made then one of the hot topics in materials science(LE et al 2018)
The perovskite structure has the chemical formula ABX3 where A-site have cube-octahedral
symmetry B-site ions are coordinated (surrounded) by an octahedron of X type ions The relative
ion size requirements for stability of the perovskite structure are quite stringent and distortion can
produce several low-symmetry distorted structures in which the coordination numbers of A
cations B cations or both are reduced (LI et al 2018)
One of the areas of approach of the perovskitas is solar cells(GRAumlTZEL 2014) This application
is a clean alternative to the current methods of generating energy so it is immensely important for
the preservation of the global environment(GRAumlTZEL 2001 ZHANG YIN 2018) Devices using
these materials have recently increased the efficiency up to 227 in solar cells with single-
junction architectures placing these compounds on the list of promising emerging
materials(AKIHIRO KOJIMA et al 2009)
The 3D halide perovskites structure is a class of bulk materials that consist of a framework of
corner-sharing metal halide octahedra that extends in all three dimensions with small cations fitting
into the unoccupied spaces between the octahedra the chemical formula for 3D perovskites is
ABX3 (LIN et al 2018) Perovskite materials exhibit many interesting and intriguing properties
from both the theoretical and the application points of view so many different properties are
commonly observed features in this family These compounds are used as sensors catalyst
electrodes and photovoltaic cells(HAO et al 2014) The perovskites used in solar cell applications
are denominated ldquoHalide perovskitesrdquo because in these compounds X is a halide element (F Cl
Br or I) This type of compounds attracts notable attention due to its high efficiency(LI et al
2017b) They have excellent optoelectronic properties fault tolerance sharp band edge and tunable
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
13
band range across the visible and near-infrared range(SALIBA et al 2018) Usually in solar cell
applications halide perovskites are commonly used as thin films but it is important to know how
their physical characteristics are defined by their crystalline structure A simple way for
understanding the properties of the organometallic halide perovskite family is classifying them by
the spatial arrangement of the halide octahedral units (MX6) as structures three-dimensional (3D)
two-dimensional (2D) one-dimensional (1D) and zero-dimensional (0D)(HUANG et al 2017
LIN et al 2018) The relationship between this spatial arrangement is shown in Figure 1
Figure 1 Typical structures of 3D 2D 1D and 0D perovskites (red spheres metal centers green
spheres halide atoms blue spheres nitrogen atoms gray spheres carbon atoms orange spheres
oxygen atoms purple polyhedrons metal halide octahedra hydrogen atoms are hidden for
clarity) as well as their corresponding conventional materials with different dimensionalities 2D
1D and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters(LIN et al 2018)
The 2D and quasi-2D perovskites structures considered as sheets or layers ripped in a specific
crystallographic direction from the 3D perovskites In particular corrugated 2D perovskites consist
of twisted sheets ripped along a crystallographic direction Metal halide layers are connected by a
perovskites ligand The general chemical formula of 2D perovskites is An-1A2BnX3n-1 and are
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
14
known as RuddlesdenminusPopper-type perovskites(HUANG et al 2017 SOE et al 2017) In 1D
perovskites the metal halide octahedra are corner-sharing edge-sharing or face-sharing to form a
1D nanowire surrounded by cations Their configurations could be either linear or zigzag and their
chemical formulas are variable depending on the connecting methods and the chosen
cations(ZHANG et al 2018a) For 0D hybrid perovskites the octahedra is isolated in the structure
These molecular perovskite units are periodically distributed in crystal lattice together with cations
to form bulk materials The general chemical formula is A4BX6 (HUANG et al 2017 LIN et al
2018 SOE et al 2017 ZHANG et al 2018a) Finally due to the strictly periodical spatial
arrangement of these metal halide structures and the packing of the species around them 2D 1D
and 0D perovskites can therefore be considered as bulk assemblies of 2D quantum wells 1D
quantum wires and 0D moleculesclusters which are structurally different from morphological 2D
nanosheetsnanoplatelets 1D nanowiresnanorods and 0D nanoparticles based on 3D
ABX3(HUANG et al 2017 LIN et al 2018 SOE et al 2017 TSAI et al 2018 ZHANG et al
2018a)
As it has been shown the diversity of structures and properties of the perovskite-related
compounds is consequence of the different anions and cations can occupy the characteristic atomic
position of this family For example a wide spectrum of potential applications was proposed by
substituting the A cation for an organic molecule the new family of organic-inorganic perovskites
is called ldquoHybrid perovskitesrdquo They have recently received extraordinary attention from the
research community because provides new applications in photoluminescence and electric
conductivity(BAYRAMMURAD SAPAROV AND DAVID B MITZI 2016) One of the most
interesting properties of hybrid perovskites is the improvement of the fast power conversion
efficiency that this material has achieved in the solar cell field
Among the methylammonium hybrid halides studied so far the most common is the
methylammonium lead triiodide (CH3NH3PbI3) It has a high charge carrier mobility and charge
carrier lifetime that allow light-generated electrons and holes to move far enough to be extracted
as current instead of losing their energy as heat within the cell Also has effective diffusion lengths
for both electrons and holes The compound CH3NH3PbI3 using an organic sensitizer increments
the efficient of photovoltaic devices from 4 to 23 in last year which is the current cell
efficiency record at this moment(ALBERO ASIRI GARCIacuteA 2016)
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
15
The crystal structure is another big different part in halide perovskites for that reason is
important to pay attention to the close packing of these compounds Thus it is useful to consider
the Goldschmidt tolerance factor concept(BAYRAMMURAD SAPAROV AND DAVID B
MITZI 2016) namely ldquotrdquo as t=(RA+RX)(radic2(RB+RX)) where RA RB and RX are the ionic radii of
cation (A) the anion (B) and halogen (X) this expression is significant because it shows the
stability and distortion in perovskites Alternatively the tolerance factor can be used to calculate
the compatibility of an ion with a crystal structure The relationship between the perovskite crystal
structure and tolerance factors (t) is shown in Table 1 while Table 2 lists the effective radius for
organic cations used to synthesize hybrid perovskites
Table 1 Relationship between the crystal structure and Goldschmidt tolerance factors (t)
Goldschmidt tolerance
factors
Structure Explanation
gt 1 Hexagonal or tetragonal A ion too big or B ion too
small
09-1 Cubic A and B ions have ideal
size
071-09 OrthorhombicRhombohedral A ions too small to fit into
B ion interstices
lt 071 Different structures A ions and B have similar
ionic radii
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
16
Table 2Effective Radii of Molecular Cations and Anions (BAYRAMMURAD SAPAROV AND
DAVID B MITZI 2016)
Even though the big impact that actually has the lead hybrid perovskites area it is important to
study all inorganic metal halide materials because they have attracted a great deal of attention over
the recent years to their ideal band gap high photoluminescence and narrow emission linewidth
Therefore we focus on the structure and properties of the Cesium-Lead-Halide perovskites family
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
17
Cesium-Lead-Halide Perovskites
Perovskites with different cesiumndashleadndashbromide stoichiometry (CsndashPbndashBr) and diverse
crystalline structures are promising candidates for new generation low-cost visible LEDs due to
their efficient emission easy production and tunability As an all-heavy-element-composed system
the CsndashPbndashBr family has similar formation energies for its variable coordination structural
phases(ZHANG et al 2018d) The advantages of this class of compounds include the versatility
of their chemical and crystallographic structures and consequently their physical properties As
stated due to the growing interest in the use of inorganic halide perovskites different synthesis
methods have been in development for years giving rise to several new compositions based on Cs-
Pb-Br This group of elements forms a 3D arrangement with chemical formula CsPbBr3 The
characteristics of this compound are the outstanding photoluminescence and optoelectronic
properties(DIROLL et al 2017 KOVALENKO PROTESESCU BODNARCHUK 2017) This
material crystallizes in the orthorhombic (Pnma) space group adopting a distorted perovskite
structure as determined by single-crystal diffraction at room temperature In this structure
PbBr64minus octahedra are tilted with respect to the conformation of the ideal perovskite
structure(STOUMPOS et al 2013a)
However under operating conditions these 3D perovskites suffers phase transformation and
instability including surface hydration and ion migration thus their reduced-dimensionality
counterparts are being increasingly investigated especially for optoelectronic applications These
new phases are related to CsPbBr3 perovskite because they have the same element constitution but
with low dimensions Different synthesis conditions made bulk single crystals members with 0D
and 2D halide structures with compositions Cs4PbBr6 and CsPb2Br5 respectively(FRANCISCO
PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI ILARIA NELLI
PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO 2017)
The first member of the CsndashPbndashBr family is the 0D structure with the Cs4PbBr6 composition In
this case the octahedra PbBr64minus are completely isolated from each other and surrounded by
cations this leads to strong quantum confinement and strong excitonminusphonon interactions This
octahedron has the same coordination that the one in CsPbBr3 perovskite Cs4PbBr6 compound
crystallizes in a trigonal system with lattice parameters a =137130(4) Aring c=173404(7) Aring with the
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
18
space group of R3c also has a band gap of Eg=3953 eV (LIU et al 2017) Early works on 0D
perovskites focused mainly on their fundamental optical absorption and photoluminescence
properties and attempted to distinguish their emission properties from those of 3D-like compounds
These studies have demonstrated that like 3D (CsPbBr3) perovskites the optical characteristics of
Cs4PbBr6 are determined by transitions between electronic states of the Pb2+ ions and their
photoluminescence results from the radioactive decay of Frenkel-type excitons at Pb2+ sites (YIN
et al 2017b) Also the zero-dimensional composite have been speculated as efficient solid-state
emitter with strong green photoluminescence by achieving quantum confinement the origin of this
study luminescence comes from PbBr64minus itself (WANG et al 2017 ZHANG et al 2017)
The other compound CsPb2Br5 this family is a ternary halogen-plumbate with close
characteristics to well-reported halide perovskites Due to its unconventional two-dimensional
structure is often obtained as secondary product during the synthesis of CsPbBr3
perovskites(TSAI et al 2016) It is important to point out that unlike CsPbBr3 that requires high
temperature for the synthesis CsPb2Br5 can be prepared easily at room temperature which is very
attractive for future applications (LI et al 2017a)
The compound CsPb2Br5 crystallizes in (I4mcm) space group and is composed of two-
dimensional layers of Pb2Br5- spaced by an isolated Cs+ cations as a consequence it is
classified as a 2D material The crystal packing of this kind of materials is characterized by layered
or corrugated sheets separated by long cations While previous reports agree on its structure and
composition they greatly diverge on the interpretation of its intrinsic optical properties which
nowadays is a subject of controversy For example there is a debate about the exact value of the
indirect band gap which was reported to be between 25 and 31 eV(DURSUN et al 2017 TANG
et al 2018) Also CsPb2Br5 exhibits a high photoluminescence being an efficient green light-
emitter with a peak located around 520 nm the emission mechanism is also a subject of
discussion(LV FANG SHEN 2018) However this compound has been investigated for potential
applications in optoelectronics
Even though several properties of the described 2D and 0D perovskites have not been yet
investigated for example the behavior of these compounds under critical conditions as pressure
and temperature Considering the growing demand to develop miniaturized and integrated
incoherent light sources it is imperative to advance in the understanding of this kind of compounds
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
19
This dissertation is organized as follows the first chapter reports the methodology employed
for preparation of the samples and describes the characterization methods In the second chapter a
new family of hybrid perovskites is presented In chapter three and four the high-pressure Raman
and photoluminescence studies of respectively CsPb2Br5 and Cs4PbBr6 perovskites are described
Finally the conclusion and perspectives are presented
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
20
Chapter 1
Experimental Section
In this chapter we described the experimental section separated in the following parts first the
synthesis of halide perovskites and secondly the characterization techniques employed for the
analysis of these compounds
Materials
The reagents used in the synthesis for perovskites were all from commercial sources The raw
materials were cesium iodate (CsI 999 ) cesium sulphate (Cs2SO4 999 ) lead bromide
(PbBr2 999 ) HBr solution (47 wt in H2O) toluene (99) and N N-dimethylformamide
(DMF) all purchased from Sigma Aldrich and Alfa Aesar
Synthesis procedures
Single crystals of halide perovskites were grown by the slow evaporation method In this
technique the compounds formed a solution of selected reagents in a solvent lefting to evaporate
under controlled conditions (CHU et al 2017 HUANG et al 2015) Using this procedure the
following single crystals were obtained
Cs4PbBr6
The precursors Cs2SO4PbBr2 were added in a small beaker in a 11 stoichiometric ratio Then
2ml of DMF and 1ml hydrogen bromide (HBr) were mixture at 80 ordmC into the beaker under constant
stirring at 480 rpm until getting a clear solution The same temperature was maintained for 1h The
resulting solution was placed to evaporate at 24 ordmC covered with parafilm containing small holes
The final crystals were washed with toluene several times
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
21
CsPb2Br5I
The precursors CsIPbBr2 were added in a small beaker in a 12 stoichiometric ratio Then 2ml
of (DMF) was mixed at 80 ordmC into the beaker under constant stirring at 480 rpm until getting a
clear solution The same temperature was maintained for 1h The resulting solution was placed to
evaporate at 24 ordmC covered with parafilm containing tiny holes The final crystals were washed
with toluene several times
(DMA)11Pb4Br19
The precursor PbBr2 was added in a small beaker with 2ml of DMF and 1ml of HBr the mixture
kept at 75 ordmC in constant stirring at 450 rpm until getting a clear solution The same temperature
was maintained for 130 h The resulting solution was placed to evaporate at 24 ordmC and the final
crystals were washed with toluene several times
(DMA)14RbPb4Br23
The precursors PbBr2Rb2SO4 were added in a small beaker with 2ml of DMF and 1ml of HBr
the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution The same
temperature was maintained for 1 hour The resulting solution was placed to evaporate at 24 ordmC
and the final crystals were washed with toluene several times
(DMA)9S4Pb5Br27
The precursors PbBr2Cs2SO4 were added in a small beaker (molar ratio 12) with 2ml of DMF
and 1ml of HBr the mixture at 80 ordmC in constant stirring at 450 rpm until getting a clear solution
The same temperature was maintained for 150 h The resulting solution was placed to evaporate
at 24 ordmC and the final crystals were washed with toluene several times
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
22
Single-crystal X-ray diffraction
Single crystal X-ray diffraction is a crystallographic method for determination of crystalline
structures (YANG et al 2017) The diffraction phenomenon is observed when a propagating
wave hits an obstacle whose dimensions are comparable to its wavelength That is the case of an
X-ray beam being diffracted when it impinges a set of planes of a crystal defined by the Miller
indices (hkl) if the geometry fulfils a quite specific condition defined by the Braggsrsquos law
119899120582 = 2119889ℎ119896119897 sin 120579 (1)
where n is an integer and is the order of the diffracted beam λ is the wavelength of the radiation
dhkl is the interplanar spacing (the perpendicular separation) of the (hkl) planes and θ is the
diffraction angle This is the principle by which diffraction data is collected from the whole crystal
The arrangement of the diffracted beams is the diffraction pattern of the crystal The Bragg
equation applied to diffraction data results in a list of dhkl values of a compound It is necessary to
allocate the appropriate hkl value to each spot in order to obtain crystallographic information This
set of data allows us to determine the unit cell of the crystal (TOBERGTE CURTIS 2013) The
X-ray diffraction pattern of a substance can be likened to a fingerprint In effect the pattern of a
single phase is unique This method is the principal technique for the determination of molecular
and crystal structure of compounds(BAIKIE et al 2013) In Figure 2 we show the equipment
used to measure the samples
Single crystal data set were collected in the Bruker D8 Venture diffractometer which was
equipped with a Photon II detector and using Mo K120572 radiation (λ=071073 Aring) A suitable crystal
for each compound was chosen and mounted on a kapton fiber using a MiTeGen MicroMount In
figure 2 we show the equipment used for each measured It is also important describe how the data
was analyzed it was indexed and integrated using SAINT V837A included in the APEX3
software Finally the structure was solved by direct methods using the SHELXT 2015 and
refinement by SHELXL 2008 included in the OLEX2
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
23
Figure 2 Single crystal diffractometer Bruker D8 VENTURE
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
24
Raman spectroscopy
The Raman effect occurs when the radiation incident is spread at different frequencies after the
light interacts with a material (LEDINSKYacute et al 2015) The process of interacting electromagnetic
radiation with a molecule is due to the annihilation and creation of phonons caused by changes in
the vibrational levels of the molecule
In a dispersion spectrum three sets of bands can be observed a central one at the same frequency
of laser called Rayleigh radiation the most intense due to the elastic dispersion and two bands
with lower intensities called Stokes and Anti-Stokes with lower and higher frequencies
respectively than the excitation one In the Rayleigh radiation the interaction with the molecule
occurs only in the electrons around the nucleus without affecting it directly so there is an elastic
scattering in which neither the photon nor the molecule suffers variations in their energy (XIE et
al 2016) The frequencies of the Raman Stokes and anti-Stokes dispersions depend on the
difference between the frequency of the incident light and the allowed vibrational frequencies
Each material will have a set of different frequencies that are characteristics of its molecular
composition(LONG 2005)
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
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BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
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CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
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CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
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CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
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2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
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DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
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DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
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DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
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53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
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Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
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GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
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HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
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HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
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HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
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HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
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HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
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JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
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KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
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KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
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LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
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LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
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LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
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LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
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LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
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NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
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PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
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QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
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RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
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SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
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SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
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SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
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SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
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(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
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SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
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TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
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TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
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TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
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TSAI H et al Design principles for electronic charge transport in solution-processed vertically
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VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
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WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
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WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
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WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
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dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
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CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
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YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
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YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
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ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
25
Figure 3 LabRam HR 800 HORIBA
Raman and PL spectra were recorded in a Labram HR 800 Horiba spectrometer equipped with
a charge-coupled device (CCD) cooled with liquid nitrogen For exciting the sample a He-Ne
(633nm) and an Ar (488 nm) lasers were used This equipment was also employed to perform
Raman experiments under high-pressure conditions using a membrane high-pressure diamond
anvil cell This device consists of a metallic gasket where the sample the ruby and the compressor
medium (mineral oil) occupy the central hole The pressure was applied through two diamonds and
controlled by an Argon (Ar) flow
Scanning Electron Microscopy (SEM)
An electron microscope uses a beam of accelerated electrons as source of illumination The
electron wavelength is 100000 times shooter than visible light photons for that reason this
equipment have a higher resolution power and can reveal the morphologic of small objects In a
scanning electron microscope (SEM) images are produced by probing the specimen with a focused
electron beam that scanned across a rectangular area of the specimen This instrument allows the
observation and superficial characterization of materials like morphologic information of the
studied compound 40
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
26
Figure 4 Scanning Electron Microscopy (SEM) QUANTA FEG 450
The crystalline morphology and the stoichiometry of the synthetized materials were investigated
by scanning electron microscopy EDX analyses were performed using a Scanning Electron
Microscope QUANTA FEG 450 available at the Central Analiacutetica of the Universidade Federal do
Cearaacute (UFC) which allows the chemical characterization of the sample(PHILIPPE et al 2015)
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
27
Chapter 2
New Family of Lead Hybrid Perovskites
The hybrid lead halides perovskites have been widely used in the research of solar cells due to
their excellent properties in photovoltaic and optoelectronic devices (LONG YAN GONG 2018)
(CHEN et al 2018a) The power conversion efficiency (PCE) has increased rapidly to more than
20 in the past years (WANG et al 2018a) The choice of organic cations and the stoichiometry
of the reaction are the most influential parameters on the orientation and deformation of the
resultant inorganic frameworks because they both have a templating influence allowing certain
structures and properties (GARCIacuteA-FERNAacuteNDEZ et al 2018) The results of the new halide
hybrid perovskites family with the organic cation dimethylammonium [(CH3)2NH2]+ (DMA)
resulting from the decomposition of DMF and located in the anionic cavities and distorted [PbX6]-
4 octahedral [(DMA)PbX3 with (X= Br I or Cl)] suggest that different stoichiometry can offer new
possibilities to achieve novel hybrid lead halide perovskites
In this context we show the structural characterization by single-crystal X-ray diffraction and
scanning electron microscopy of three new hybrid lead halide perovskites designed as stated by
combining [PbBr6]-4 octahedra and DMA We obtained compounds which are new and original in
structure and formula these compositions are (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27
Remarkably we have observed that all new hybrid lead halide perovskites are stable at room
temperature Another important aspect to highlight is the fact these compounds crystallize in
different space groups they display crystal structures even though they have significant differences
in cell parameters All structures consist on single-layered lead halide frameworks with DMA
cations Br- anions and Rb1+ and S+2 isolated atoms This material has halide octahedra formed by
Pb+2 cations with octahedral coordination through six halide ligands making the [PbBr6]4-
composition
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
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FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
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LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
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SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
28
Figure 5 View of (a) crystal unit structure of (DMA)11Pb4Br19 at room temperature along the a
b and c axis and (b) 1x2x2 bounding octahedrons
The crystal arrangement of the compound (DMA)11Pb4Br19 has bounded halide octahedra
[PbBr6]4- the compound crystallizes in a monoclinic symmetry with cell parameters a =108017(3)
Aring b =278009(8) Aring c =248172(7) Aring β =914880(10) deg and V =74500(4) Aring3 Z = 4 and
space group P21n As we can see in the Figure 5b the octahedral framework displays a peculiar
arrangement this one is composed by two different types of octahedral 1D chains The chain
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
29
formed by six octahedra bounded through corner and faces is denominated -chain whereas the
-chain has just two octahedra sharing a corner
Figure 6 View of (a) crystal unit structure of (DMA)14Pb4Br23 at room temperature along the a
b and c axis and (b) 2x1x2 bounding octahedrons
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
30
The structure of the (DMA)14RbPb4Br23 exhibits an orthorhombic crystalline system with cell
parameters a = 438990(3) Aring b =156404(10) Aring c =145021(9) Aring V =99571(11) Aring3 Z =4 and
space group Pbcn This compound contains four independent Pb2+ cations twenty-three Br- anions
one Rb+ atom and twenty-three DMA cations both isolated this structure is shown in Figure 6(a)
This hybrid perovskite has a framework with chains of [PbBr6]4- octahedra it is shown in figure
6(b) Two octahedral motifs can be identified a -chain 1D structure formed by two corner sharing
octahedrons and isolated octahedrons with 0D dimensionality
Figure 7 View of (a) crystal unit structure of (DMA)9S4Pb5Br27 at room temperature along the
a b and c axis and (b) 1x2x2 bounding octahedrons
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
31
Finally the (DMA)9S4Pb5Br27 structure show in Figure 7(a) crystallizes in the monoclinic
crystal system with a =109761(4) Aring b =329494(12) Aring c =151073(6) Aring β =972490(10)deg Z = 4
and space group P21n This structure contains independent five Pb2+ cations twenty-seven Br-
anions four S+2 atom and nine DMA cations isolated The framework of this structure is formed
by 1D chains of four corner sharing collinear octahedrons denominated by -chain and 0D isolated
octahedrons
One important part of each structure is they have disordered octahedra and DMA molecules
The best indicator for disorder in a crystal structure is when the compound has big anisotropic
displacement or residual electron density Most of disorder problems can be diagnosed by looking
at the size andor shape of the displacement parameters or by finding higher noise in Q-peaks which
make unreasonable interactions SHELX as a program warn about the atoms appear to be split
which is good sing for looking disorder problems Typical disorder occurs around freely rotating
bonds or in solvent channels that are larger than the solvent molecules accommodating them
together in the same site very near or with an absence (SARJEANT 2018)
To solved this problem first we investigated the geometry of the site and chemistry involved
(stoichiometry) with the list of atoms to identify the disordered motifs After located the disordered
atoms subsequently we used the command EXYZ in SHELX to constrain the displacement
parameters and made them equal with this we have a separated list where the coordinates and
displacement parameters are identical then create a second atom directly overlaid on the first set
After we edit the value (distortion atom) either to set it manually to a known value (real place) or
to a free variable to be refined Later we refine the structure as usual (to mixture both list) paying
close attention to size of the displacement parameters
As we can see each crystalline framework displays a peculiar arrangement where their
respectively octahedra form 0D andor 1D chains (bounding through corner andor faces)
(KRISHNAMURTHY et al 2018) A combination of chains of different dimensionality is a novel
characteristic in this type of compounds this is a relevant packing because the optical properties
of perovskite-related compounds depend on the confined excitons in the octahedral motifs
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
32
Table 3 presents a comparison of the results obtained in this work for lead halide perovskites
(DMA)11Pb4Br19 (DMA)14RbPb4Br23 and (DMA)9S4Pb5Br27 with the structure reported by Garcia
et al (GARCIacuteA-FERNAacuteNDEZ et al 2018) In the current table we can find the cell parameters
space group refinement informations and dimensions of the crystals
Table 3 Reported crystal parameters for each novel hybrid perovskites
Empirical
formula
((DMA)7Pb4Br15)(GARCIacuteA
-FERNAacuteNDEZ et al
2018)
(DMA)11Pb4Br19 (DMA)14RbPb4Br2
3
(DMA)9S4Pb5Br2
7
Formula
weight
235006 276538 305640 335828
Temperatur
e
275(2) K 302(2) K 273(2) K 273(2) K
Wavelength 071073 Ǻ
Crystal
system
Monoclinic Monoclinic Orthorhombic Monoclinic
Space group P21c P21n Pbcn P21n
Unit cell
dimensions
a=170859(3) Ǻ
b=196358(3) Ǻ
c=164307(3) Ǻ
β=105719(1)
a=108017(3) Ǻ
b=278009(8) Ǻ
c=248172(7) Ǻ
β=914880(10)
a=43899(3) Ǻ
b=156404(10) Ǻ
c=145021(9) Ǻ
a=109761(4) Ǻ
b=329494(12) Ǻ
c=151073(6) Ǻ
β=972490(10)
Volume 530627(16) Ǻ3 74500(4) Ǻ3 99571(11) Ǻ3 54200(4) Ǻ3
Z 4 2
Density 2942 Mgm3 2466 Mgm3 2039 Mgm3 2058 Mgm3
Absorption
coefficient
23967 mm-1 19225 mm-1 16472 mm-1 17774 mm-1
F(000) 4168 4808 5288 2875
Crystal size 024x006x002 mm3 022x0136x011
6 mm3
0214x0185x013
mm3
028x0164x016
mm3
Theta range
for data
collection
1615 to 2639
235 to 2385
237 to 2742
252 to 2367
Refinement
method
Full-matrix least-squares on F2
R indices
(all data)
R1=01816 wR2=01765
R1=0951
wR2=01207
R1=01504
wR2=03752
R1=00854
wR2=02090
Type of
chain
2D chain α β β γ
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
33
It has been demonstrated that single crystal of hybrid lead halide perovskites can be obtained by
slow evaporation method To define the effective stoichiometry and morphology of each compound
we have used scanning electron microscopy on each of the novel hybrid perovskites As an
example Figure 8 shows the results obtained for the single crystal (DMA)11Pb4Br19 which was
divided in 3 parts The Line 1 shows a uniform surface morphology in the crystal O elemental
mapping images of Pb Br C and N can be observed in the Line 2 indicating the particles
distribution in the following spectrum where correspond to the perovskite phase In the Line 3 we
have a qualitative map for all most constituent elements
In conclusion we have obtained three new perovskite related compounds and the corresponding
crystalline structures have been reported These perovskites have differences in the [PbBr6]4-
octahedron framework exhibiting several 0D 1D and 2D dimensionalities which is potential
feature for the development of novel applications and the raising of new properties
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
34
Figure 8 Line 1 (DMA)11Pb4Br19 morphology Line 2 sum of composition element map and
each element map and Line 3 Spectrum map sum for all constituent element in (DMA)11Pb4Br19
perovskite
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
35
Chapter 3
CsPb2Br5I under High-pressure
The single-crystal X-ray analysis revealed that the obtained CsPb2(Br085I015)5 samples presents
a tetragonal structure belonging to 1198684119898119888119898 (ITA number 140) space group with lattice parameters
119886 = 85291(8) Aring and 119888 = 153428 (19) Å and four molecular units per unit cell The
CsPb2(Br085I015)5 structure is very similar to those reported for CsPb2Br5 (NAZARENKO et al
2017 WANG et al 2016a) and CsPb2Cl5 (CHEN et al 2018b KIM JO OK 2009) However
the insertion of I- ion induces an increasing into the bond lengths and as consequence the cell
parameters of CsPb2(Br085I015)5 are bigger in comparison to those 119886 = 84833(10) Aring and 119888 =
151830 (18) Å reported for CsPb2Br5 Besides the alterations on the bond lengths the single
crystal X-ray analysis also revealed that the I- presence induces a degree of disorder on
CsPb2(Br085I015)5 where the I- cations replaces the Br- atoms on 16l site On the other hand the
second Br site (4c) is ordered with Br- ions aligned with Cs atoms along c axis (Figure 9 (c)) In
this way the CsPb2(Br085I015)5 structure can be described as a sandwich configuration in which
[Pb2(BrI)5]- layers intercalated by Cs+ ions (Figure 9 (a)) Thus the [Pb2(BrI)5]
- layers are
constituted by one Pb2+ coordinates with four Br- or BrI- forming elongated decagon (see Figure
9) The disordered BrI 16l site is the one locate at the upper and lower edges of [Pb2(BrI)5]- layer
while the ordered 4c site occupied by Br- ions are located at the middle of those layers This atomic
configuration also induces an increased in the [Pb2(BrI)5]- layer width of 3994 Aring in comparison
to the one of 3921 Aring presented by CsPb2Br5
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
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BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
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CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
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2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
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DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
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FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
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Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
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HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
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HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
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JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
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KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
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Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
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LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
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LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
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LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
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SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
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SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
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VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
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WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
36
Figure 9 CsPb2(Br085I015)5 unit cell
EDX analyzes were carried out to determine the distribution of I- cations on crystal surface
Figure 10 shows a EDX image of a CsPb2(Br085I015)5 single crystal The EDX images showed that
the I- cations are uniformly distributed on all crystal surface (Figure 10 (a) and (b)) implying that
the synthetized crystals have good homogeneity and the border analysis shows no concentrations
of any structural ion or sub-phases as observed for CsPb2Br5 (WANG et al 2018b) (Figure 10 (c))
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
37
Figure 10 CsPb2Br426I074 single crystal EDX Images
Raman spectroscopy is known as a sensitive technique for detecting phase transitions or subtle
structural rearrangements Thus in order to investigate any structural modification due to pressure
increase Raman measurements were performed to investigate single-crystals of CsPb2(Br085I015)5
up to 708 GPa Figure 11 presents the representative unpolarized Raman spectrum recorded for a
single-crystal of CsPb2Br426I074 sample at ambient conditions Considering the group theory
analysis based on the site occupation in this tetragonal structure 13 Raman-active modes are
predicted whose the distribution in terms of irreducible representations for the D4h group factor at
the Γ point of Brillouin zone (ROUSSEAU BAUMAN PORTO 1981) is
31198601119892⨁21198611119892⨁31198612119892⨁5119864119892 (see table 4) As Figure 11 shows we observed 6 from those 13
expected Raman-active modes By means of theoretical calculations and confirmed by
experimental measurements Hadjiev et al(HADJIEV et al 2018) assigned the symmetry for the
observed phonons for CsPbBr5 which belongs to the same D4h group factor In this way the modes
observed at 65 103 and 143 cm-1 have the B2g symmetry those located at 81 and 132 present A1g
symmetry and the one located at 76 cm-1 have B1g symmetry Some modes present a lower
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
38
frequency in comparison to those observed by Hadjiev et al this fact is due to BrI disorder at 16l
site which increases the reduced mass and consequently decreases the vibrational frequency
Table 4 Distribution of vibrational modes based on group theory analysis for tetragonal
CsPb2(Br085I015)5
Ion Site Symmetry Contribution
Pb 8ℎ 1198622119907prime 1198601119892⨁1198602119892⨁1198602119906⨁1198611119892⨁1198611119906⨁1198612119892⨁119864119892⨁2119864119906
Cs 4119886 1198634 1198602119892⨁1198602119906⨁119864119892⨁119864119906
Br1 4119888 1198624ℎ 1198601119906⨁1198602119906⨁2119864119906
Br2I 16119897 119862119904119889 21198601119892⨁1198601119906⨁1198602119892⨁21198602119906⨁1198611119892⨁21198611119906⨁21198612119892⨁1198612119906⨁3119864119892⨁3119864119906
Γ119879119874119879 = 31198601119892⨁21198601119906⨁31198602119892⨁51198602119906⨁21198611119892⨁31198611119906⨁31198612119892⨁1198612119906⨁5119864119892⨁8119864119906
Γ119860119888 = 1198602119906⨁119864119906
Γ119868119877 = 41198602119906⨁7119864119906
Γ119877119886119898119886119899 = 31198601119892⨁21198611119892⨁31198612119892⨁5119864119892
Γ119878119894119897 = 21198601119906⨁31198611119906⨁1198612119906
Figure 11 Representative unpolarized Raman spectrum of CsPb2(Br085I015)5 at room pressure
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
39
Figure 11(a) shows selected stacked Raman spectra of CsPb2(Br085I015)5 under hydrostatic
compression All six assigned Raman-active vibrational modes in the range between 60 and 180
cm-1 at ambient conditions were analyzed under increasing pressure All vibrational modes
presented a continuous shift toward higher wavenumbers due to lattice contraction while the
overall signature of Raman spectra is maintained as the original state up to 176 GPa A new
vibrational mode appears around 85 cm-1 at 193 GPa (Figure 11(b)) The appearance of this mode
is associated to the occurrence of a structural phase transition Around 52 GPa we note the
disappearance of Eg B2g and B2g modes initially located at 103 and 143 cm-1 besides the
emergence of a new mode around 84 cm-1 The observed variation on the number of vibrational
modes evidences that CsPb2Br426I074 undergoes another phase transition between 51 and 55 GPa
Above 55 GPa the Raman spectra is maintained until 708 GPa without any evidence of amorphous
state or additional phase transitions Upon pressure releasing the Raman spectrum at 069 GPa
returned to the initial state matching well with the initial positions and the relative intensities
between the vibrational modes were recovered indicating that the two structural phase transitions
are reversible
Figure 12 a) Pressure dependent Raman spectrum of CsPb2(Br085I015)5 b) Pressure dependent
phonon positions
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
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BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
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CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
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CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
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2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
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DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
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DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
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vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
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Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
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HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
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HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
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HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
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HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
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HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
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JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
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KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
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KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
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KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
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LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
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LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
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LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
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LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
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LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
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NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
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SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
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SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
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SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
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(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
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TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
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TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
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VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
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WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
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WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
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WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
40
The CsPb2(Br085I015)5 single crystals emission spectra were studied under 488 nm laser
excitation The results showed a bright green PL band centered at 519 nm with full width at half
maximum (FWHM) of 20 nm under ambient conditions these results are consistent with those PL
emission peaks reported for other halide-perovskites as CsPbX3(X=Cl Br)(STOUMPOS et al
2013b VOLOSHINOVSKII MYAGKOTA LEVITSKII 2005) Cs4PbBr6 (DE BASTIANI et al
2017b) and FAPbBr3 (HANUSCH et al 2014)
Despite the similarities on crystal structure the CsPb2(Br085I015)5 single crystals presented a
strong PL emission peak whereas the CsPb2Br5 did not present any signal of PL emission Wang
et al (WANG et al 2018b) affirms that millimeters size crystals of CsPb2Br5 should be transparent
and non-emissive while very small crystals which size is in order of microns present edge emission
related to contamination of CsPbBr3 nanocrystals(LI et al 2017c QIN et al 2017 RUAN et al
2017) In case of CsPb2(Br085I015)5 the EDX results showed that the synthetized crystals present a
good homogeneity indicating that the observed PL emission in CsPb2(Br085I015)5 are not related to
presence of sub-phases and probably being related exclusively to presence of I cation on BrI
disordered site
The Figure 12 (a) shows the stacked PL spectra obtained for CsPb2(Br085I015)5 under pressure
increase The two very intense peaks located around 522 nm in all PL spectra are related to Raman
active modes of the diamonds of the high pressure cell The PL intensity showed a gradual increase
upon pressure until reaches a maximum value at 133GPa from this point the intensity decrease
until the pressure of 271 GPa where the PL emission vanish (Figure 12 (b)) This changing on
intensity around 133 GPa can be related to changes on structure or a starting point of phase
transitions Besides the changes on PL emission intensity the maximum position also showed a
gradual and linear red shift up to 176 GPa (Figure 12 (c)) At this point the PL undergoes a jump
from 526 to 528 nm at 193 GPa from which a sudden blue shift follows up to the pressure reaches
271 GPa where the PL peak disappear The abrupt change in the PL peak pressure behavior has
been understood as the crystalline structure undergoing a phase transition as observed in several
halide perovskite pressure dependent studies(JAFFE et al 2016 SZAFRAŃSKI KATRUSIAK
2016 ZHANG et al 2018c ZHANG ZENG WANG 2017b) Thus these results are indicative
that the CsPb2(Br085I015)5 undergoes a phase transition at 176 GPa reinforcing first phase transition
observed on pressure dependent Raman analysis showed above
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
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BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
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BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
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KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
41
Figure 13 Pressure dependent a) PL spectra b) PL intensity and c) PL emission center
Upon decompression at 069 GPa the PL peaks returns to the original state (Figure 13 (a)) with a
bright green PL peak centered at 521 nm and 23 nm of width Which is an indicative that the loss
of PL emission at high pressures also is a reversible phenomenon
In conclusion the structure CsPb2(Br085I015)5 presents tetragonal symmetry with space group
1198684119898119888119898 Shows occupational disorder in the 16l site and presents two-phase transitions around
18 and 53 GPa
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
42
Chapter 4
Pressure-Induced enhanced photoluminescence and Raman
scattering study of the zero dimensional Cs4PbBr6 lead
halide perovskite
As discussed previously Cs4PbBr6 is classified as a 0D-Perovskite structure which is composed
of isolated (PbBr6)4minus octahedra interspersed with Cs+ cations Having that in mind the (PbBr6)
4minus
octahedra can be treated as an isolated molecular group in the crystal Therefore the vibrational
modes of this crystal can be classified according the translational librational and intramolecular
vibrations of the (PbBr6)4minus octahedral group In order to identify the symmetry and predict the
Raman and infrared activity of each vibrational mode of Cs4PbBr6 the correlation method was
applied (FATELEY et al 1972 ROUSSEAU BAUMAN PORTO 1981)
The correlation method requires the knowledge of the number of formula units in the Bravais
cell (ZB) which is equal to Z (the number of the formula units per crystallographic unit cell) divided
by the number of lattice points (LP) determined by the designation of the space group Single
crystals of Cs4PbBr6 crystallizes in the trigonal structure with space group 1198773119888 Its Bravais cell
contains two formula units (ZB = 2) with N = 22 atoms
The Wyckoffrsquos site positons and the symmetry of the constituent ions are given in the Table 5
Since the site symmetry of the molecular group is the symmetry of the central atom the (PbBr6)4minus
octahedral ion occupies a S6 site symmetry
Table 5 Wyckoffs site positions of the atoms in the Cs4PbBr6 single crystal
Ion Wyckoff Site Site Symmetry
119914119956120783 6a 1198633
Pb 6b 1198786
119914119956120784 18e 1198622
Br 36f 1198621
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
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ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
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BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
43
The isolated (PbBr6)4minus octahedral ion has Oh symmetry and its vibrational motions may be
designated by the standard Herzberg notation(HERZBERG 1945) 1198601119892 (1205841) 119864119892(1205842) 1198651119906 (1205843)
1198651119892 (rotation) 31198651119906 (translation 1205843 1205844 ) 1198652119892 (1205845) 1198652119906 (1205846) The representations of Oh specify the
motions of the (PbBr6)4minus octahedral ion and the designations in parenthesis after each
representation are the standard Herzberg notation (1205841 1205842 and 1205843 are the stretching modes of the
bonds Pb ndash Br and 1205844 1205845 and 1205846 are the deformation modes of the Br ndash Pb ndash Br angles)
Table 6 Correlation table for Cs4PbBr6 The degrees of vibrational freedom for a given site
species γ is given by the symbol 119891120574 The translational and rotational degrees of freedom of the
(PbBr6)4minus octahedra become translational and librational lattice modes in the crystal
Table 6 lists each of the Oh representations of the (PbBr6)4minus octahedral ion The effect of the
lowering of the symmetry is determined by the correlation between the Oh and the S6
representations (site symmetry) and finally with the 1198633119889 one (crystalline symmetry)
The correlation method yields the irreducible representations at the Γ-point phonon modes In
the Table 6 the degrees of vibrational freedom for a site species γ is given by the symbol 119891γ The
crystal has 3N = 66 vibrational freedom degrees including 3 acoustics (120548119860119888119900119906119904119905119894119888 = 1198602119906 oplus 119864119906)
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
44
and 63 optical modes (120548119900119901119905119894119888 = 41198601119892 oplus 51198601119906 oplus 61198602119892 oplus 61198602119906 oplus 10119864119892 oplus 11119864119906) Among
optical modes only 1198601119892 and 119864119892 are Raman actives and 1198602119906 and 119864119906 are IR actives The vibration
modes related to the octahedra are (120548119871119894119887119903119886119905119894119900119899 = 1198601119892 oplus 1198602119892 oplus 2119864119892) Besides these modes there
are 10 silent modes 120548119878119894119897119890119899119905 = 51198601119906 oplus 51198602119892 which are neither Raman nor IR active modes
The pressure effect on lead halide 3D-perovskite have been drawn extensive attention and
demonstrating an unavoidable impact on the optical properties of these structures (BEIMBORN et
al 2018 WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) However on the other hand at the best of our knowledge the
pressure effect on 0-D perovskites structures have not been reported Another important
observation worth noting is that the dimensionality of (PbBr6)4minus octahedron strongly influences its
optical properties(ZEWEN XIAO et al 2017)(ZHANG ZENG WANG 2017a) Thus
considering this we carried out high-pressure optical photoluminescence and Raman experiments
on Cs4PbBr6 0D-perovskite to investigate the pressure-induced optical evolution
40 60 80 100 120 140 160 180 200 220 240 260 280 300
Ram
an I
nte
snsi
ty (
au
)
Wavenumbers (cm-1)
Experimental
Lorenztian
Calculated
45
4856
61
6975
84
107
124
136
153
179
Figure 14 Raman spectrum of Cs4PbBr6 0D-Perovskite single crystal observed at room
temperature and pressure The red continuous line represents the result of the decomposition of
the spectrum with a set of Lorentzian line profiles (blue lines)
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
45
According to the group theory we expect up to 14 Raman (120548119877119886119898119886119899 = 41198601119892 oplus 10119864119892) and 17
infrared (120548119868119877 = 61198602119906 oplus 11119864119906) active modes at room temperature and pressure in the trigonal
phase As showed in Figure 14 12 Raman active modes described by the group theory were
observed experimentally which is a good number of modes considering we have broad and subtle
bands that induce mode overlaps Some of the observed modes can be assigned according to
previously reported works on Cs4PbBr6 and compounds with similar compositions and molecular
groups Therefore the modes at 84 cm-1 and 124 cm-1 are attributed to the PbminusBr rocking modes
in the [PbBr6]4minus octahedron (YIN et al 2017b) which is agree to group theory showed in Table 6
where was predicted two 1205845 modes associated to octahedron deformation with 119864119892 symmetry The
mode located around to 136 cm-1 is assigned to the PbminusBr stretching modes(YIN et al 2017b
ZHANG et al 2018b) According to the group theory this mode might be 1205841 with 1198601119892 symmetry
or 1205842 with 119864119892 symmetry
The pressure-dependence Raman spectra of the Cs4PbBr6 from ambient condition up to 1085
GPa are shown in Figure 15(a) As pressure increases all Raman peaks move continuously along
the high-frequency direction However with respect to the lower pressure values from to 071 GPa
a remarkable red shift in the profile of the spectra is observed When the pressure reaches 036
GPa the Raman spectra exhibit some significant changes the vibrational modes at 61 and 153 cm-
1 disappear and the modes around to 75 and 84 cm-1 become in a single broadened mode A similar
high pressure behavior with structural phase transitions at lower pressure values eg at 04 and
056 GPa were obeserved for lead-based halide inorganic 3D perovskites MAPbBr3 and FAPbBr3
respectively (WANG WANG ZOU 2016 WANG et al 2015) which is very close to one on the
0D Cs4PbBr6 crystal However for lead-based halide organic 3D perovskites such as CsPbBr3
(ZHANG ZENG WANG 2017a) and CsPbCl3 (CSPBCL et al 2018) the structural phase
transitions are observed starting approximately around to 13 GPa Thus the inorganic Cs4PbBr6
crystal requires lower pressures for phase transitions which indicated that it is much more
compressible under external pressures than those another lead-based halide inorganic cited above
As shown in Figure 15 an interesting behavior on the Raman modes at 22 GPa is observed the
splitting of the mode around to 55 cm-1 in two modes at 54 and 57 cm-1 which may indicate a
structural phase transition In general a similar pressure-induced structural phase transition
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
46
behavior is observed around to 20 GPa on all like structures reported so far (WANG et al 2016b
2015 WANG WANG ZOU 2016 ZHANG et al 2018b) Another phase transition can be
inferred near to 657 GPa This phase transition is subtle looking directly at the Raman spectra in
Figure 15 but can be clearly observed from the evolution of the modes with the pressure in Figure
15(b) However a more precise characterization can be obtained by means of a pressure X-ray
diffraction experiment
Upon further increase of pressure up to 353 GPa a clear change in the phonon spectrum of the
crystal is observed As showed in Figure 15(a) the modes associated to the lattice become broader
some of them disappear eg the modes around 92 and 106 cm-1 and a new mode arises at 117 cm-
1 due to the widening of the mode at 110 cm-1 (see Figure 15(b)) The most characteristic feature
is however the significant lowering and broadening intense as well as the red shift of the 1205845 mode
at 84 cm-1 assigned to octahedron Thus these results indicate a dramatic change in the crystal
structure for this pressure value which is highly relevant because the PbBr6 octahedra play a key
role in the optical properties of these structures
Figure 15 (a) Raman spectra measurements of Cs4PbBr6 0D-PRS single crystal under high
pressure conditions up to 1085 GPa Several pressure-induced phase transitions are observed
(b)Wavenumber vs pressure plots of the Raman modes observed in the Cs4PbBr6 crystal for
compression experiments The vertical lines indicate the pressures at which Cs4PbBr6 undergoes
phase transitions
0 1 2 3 4 5 6 7 8 9 10 11 1240
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
Wa
ve
nu
mbe
rs (
cm
-1)
Pressure (GPa)
(036 500)
40 60 80 100 120 140 160 180 200 220 240 260 280
ʋ1ʋ5
036 GPa
Release
1085 GPa
1015 GPa
968 GPa 921 GPa
758 GPa
708 GPa 680 GPa
657 GPa 632 GPa 600 GPa 550 GPa
514 GPa 473 GPa
390 GPa 428 GPa
353 GPa
325 GPa
290 GPa 275 GPa 248 GPa 220 GPa 190 GPa
150 GPa 123 GPa 100 GPa
071 GPa
0 GPa
Ram
an I
nte
nsi
ty(a
u)
Wavenumber (cm-1)
ʋ5
(a) (b)
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
47
Is worth note that some of the modes that were once lost during compression from 353 to 428
GPa reappeared at 473 GPa and we can also notice a subtle blue shift of the octahedral mode near
84 cm-1 As the applied pressure exceeds 921 GPa the broad modes significantly decrease in
intensity accompanied by broadening and disappearance of some initial modes implying the onset
of deteriorated crystal crystallinity due significant to disorder of the PbminusBr network structure under
high pressure
Figure 16 (a) Photoluminescence spectra of Cs4PbBr6 as a function of pressure (b) PL emission
center and intensity
In order to better understanding the pressure induced PL behavior we plot in the figure 16(a)
the selected photoluminescence spectrarsquos as a function of pressure The Cs4PbBr6 exhibits a single
PL centered at 506 nm in good agreement with recent reports which exhibits a peak around to 515
nm(CHA et al 2017 DE BASTIANI et al 2017a SAIDAMINOV et al 2018 SETH
SAMANTA 2017 YIN et al [sd]) While in the organic-inorganic lead halide 3D-perovskite
early reported(WANG et al 2016b 2015 WANG WANG ZOU 2016 ZHANG et al 2018b
ZHANG ZENG WANG 2017a) the PL is suppressed by the hydrostatic pressure in the Cs4PbBr6
0D-perovskite single crystal present an anomalous behavior under high pressure conditions The
PL peak showed a gradual red shift of up to 10 Gpa when the pressure was increased Above this
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
48
pressure the peak exhibits a blue shift which is accompanied by the decreasing of the PL intensity
The peak completely disappears above 43 GPa but a closer inspection of the pressure dependence
of emission peak shows that above this pressure the peak should be located below the wavelength
of the excitation laser From our results it is not possible to conclude if the decreasing of the
intensity of the PL emission is related to the pressure or to the reduction of the excitationemission
energy difference Regarding to the effect of the structural phase transitions the changes in both
the intensity and wavelength does not seems to be directly associated with the structural phase
transitions but to the local distortion of the PbBr4- octrahedra rather than the crystal symmetry
This could be consequence of the exciton confinement characteristics of the 0D perovskites and
could be a valuable mechanism to tune the PL emission by using hydrostatic pressure
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
49
Conclusions
The lead halide perovskites exhibit promising properties in different fields like solar cells
which is an alternative to generate energy preserving the global environment Halide perovskites
presents high efficiency and excellent optoelectronic properties due their crystalline structure and
spatial arrangement of octahedral units The configurations of dimensionality in perovskites
structures are classified in 2D quantum wellsnanoplatelets 1D quantum wiresnanorods and 0D
clustersnanoparticles
The new hybrid perovskites are compounds with characteristics that different organic-inorganic
cation can occupy the same atomic positions this property increase the efficient of photovoltaic
devices The principal focus of this work was study of critical effect as pressure under low
dimensional halide perovskites to achieve this goal our investigation was based in synthesis of
these compounds by the slow evaporation technique and his characterization by single crystal X-
ray diffraction Raman and PL analyses
We have successfully produced five different compounds with different crystalline structures
three of them are novel hybrid lead halide perovskites as (DMA)11Pb4Br19 (DMA)14RbPb4Br23 and
(DMA)9S4Pb5Br27 compositions these compounds are low dimensional perovskites based on
frameworks of the same [PbBr6]-4 octahedra Even though they have the same [PbBr6]
-4 group
they display peculiar and different arrangements where the structures had a combination of two
low dimensional motifs 1D chains of corner andor faces shared octahedral and isolated 0D
octahedral This distinguishing behavior is a new characteristic reported here for the first time
which could be relevant for future applications because perovskites properties depend on the
dimensional structure
The CsPb2(Br085I015)5 crystals showed a tetragonal structure belonging to 1198684119898119888119898 space group
with four molecular units per unit cell Single crystal X-ray analysis showed that the 16l site can
be occupied by Br- or I- ions creating a disorder in this site while the 4c site is ordered with Br-
ions aligned with Cs atoms along c axis The atomic configuration can be described as a sandwich
configuration in which [Pb2(BrI)5]- layers are intercalated by Cs+ ions in good agreement with
those reported for CsPb2X5 (X = Cl Br) EDX analysis revealed that CsPb2(Br085I015)5 crystals
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
50
have good homogeneity without any concentration of secondary phases along crystal surface The
PL emission of CsPb2(Br085I015)5 single crystals was studied under 488 nm laser excitation
showing a bright green PL emission exhibiting standard a Gaussian shape centered at 519 nm with
full width at half maximum (FWHM) of 20 nm at ambient conditions consistent with those PL
emission spectra reported for other halide-perovskites Based on EDX images the PL emission of
CsPb2(Br085I015)5 are related to I- cation and not due to secondary phases as observed as reported
for CsPb2Br5
The unpolarized Raman spectrum of CsPb2(Br085I015)5 at ambient conditions presented 6 of
those 13 predicted modes based on group theory analysis The pressure dependent Raman spectra
were carried out to monitor the changes in the crystalline structure under high-pressure revealing
two phase transitions around 18 and 53 GPa being the number of transitions in good agreement
with the pressure dependent behavior of halide-perovskites the structural evolution must be better
defined by performing high-pressure XRD analysis The pressure dependent PL emission also
showed a gradual increase of intensity upon pressure increase this behavior is held until 133 GPa
where the PL peak reaches a maximum value From this point the intensity decrease until the
pressure of 271 GPa where the PL emission vanishes Besides the intensity changes the PL
position also showed a gradual and linear red shift up to 176 GPa where a split from 526 to 528
nm was observed at 193 GPa From this point a sudden blue shift follows up to the pressure reaches
271 GPa The increase abrupt change pressure depend behavior around 176 GPa confirms the first
phase transition observed on Raman measurements
Also we investigated the effects of pressure on the crystalline structure and optical PL of the
single crystal Cs4PbBr6 The results suggest that the single crystal under study undergoes a
pressure-induced structural phase transition at low-pressure values very close those were observed
for lead-based halide inorganic 3D perovskites Other subtle changes in the Raman modes were
observed at 22 GPa and 657 GPa which can be associated to structural phase transitions From
353 GPa to 43 GPa a significant change in crystal structure were observed The modes associated
to octahedra undergo clear changes which is very interesting once the octahedra play a key role in
the optical properties However significant changes were not observed in the PL for this value
pressure but the peak completely disappears above 43 GPa The PL peak showed a gradual red
shift of up to 10 Gpa then a blue shift accompanied by the decreasing of the intensity when the
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
51
pressure was increased The results show that the pressure-induced PL behavior is associated to the
local distortion of the PbBr4- octahedra and is not related to structural phase transitions Therefore
our high-pressure studies of the structural stability and PL of Cs4PbBr6 0D-perovskite shed light
on a valuable mechanism to tune the PL emission by using hydrostatic pressure
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
52
References
AKIHIRO KOJIMA et al Organometal Halide Perovskites as Visible- Light Sensitizers for
Photovoltaic Cells J Am Chem Soc v 131 n October p 6050ndash6051 2009
ALBERO J ASIRI A M GARCIacuteA H Influence of the composition of hybrid perovskites on
their performance in solar cells Journal of Materials Chemistry A v 4 n 12 p 4353ndash4364
2016
BAIKIE T et al Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for
solid-state sensitised solar cell applications Journal of Materials Chemistry A v 1 n 18 p
5628 2013
BAYRAMMURAD SAPAROV AND DAVID B MITZI OrganicminusInorganic Perovskites
Structural Versatility for Functional Chemical Reviews v 116 p 4558ndash4596 2016
BEIMBORN J C et al Pressure Response of Photoluminescence in Cesium Lead Iodide
Perovskite Nanocrystals 2018
CHA J-H et al Photoresponse of CsPbBr 3 and Cs 4 PbBr 6 Perovskite Single Crystals The
Journal of Physical Chemistry Letters v 8 n 3 p 565ndash570 2017
CHEN F et al Structure Evolution of CH3NH3PbBr3 Single Crystal Grown in N N-
dimethylformamide Solution Crystal Growth amp Design p acscgd8b00256 2018a
CHEN Y et al Synthesis Crystal Structure and Optical Gap of Two-Dimensional Halide Solid
Solutions CsPb 2 (Cl 1ndash x Br x ) 5 Inorganic Chemistry v 2 p acsinorgchem8b01572 jul
2018b
CHU K et al An ABX3organicndashinorganic perovskite-type material with the formula
(C5N2H9)CdCl3 Application for detection of volatile organic solvent molecules Polyhedron v
131 p 22ndash26 2017 CSPBCL M P et al Pressure-Induced Structural Evolution and Optical
Properties of The Journal of Physical Chemistry C v 122 p 15220ndash15225 2018
DE BASTIANI M et al Inside Perovskites Quantum Luminescence from Bulk Cs4PbBr6 Single
Crystals Chemistry of Materials v 29 n 17 p 7108ndash7113 2017a
DIROLL B T et al High-Temperature Photoluminescence of CsPbX 3 (X = Cl Br I)
Nanocrystals Advanced Functional Materials v 27 n 21 p 1606750 2017
DURSUN I et al CsPb2Br5 Single Crystals Synthesis and Characterization ChemSusChem v
10 n 19 p 3746ndash3749 2017
FATELEY W G et al Infrared and Raman selection rules for molecular and lattice
vibrations 1972
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
53
FRANCISCO PALAZON SEDAT DOGAN SERGIO MARRAS FEDERICO LOCARDI
ILARIA NELLI PRACHI RASTOGI MAURIZIO FERRETTI MIRKO PRATO R K AND L
M From CsPbBr3 Nano-Inks to Sintered CsPbBr3minusCsPb2Br5pdf The Journal of Physical
Chemistry C v 121 p 11956ndash111961 2017
GARCIacuteA-FERNAacuteNDEZ A et al 7Pb4X15(X = Cl-and Br-) 2D-Perovskite Related Hybrids with
Dielectric Transitions and Broadband Photoluminiscent Emission Inorganic Chemistry v 57 n
6 p 3215ndash3222 2018
GRAumlTZEL M Photoelectrochemical cells Nature v 414 n 6861 p 338ndash344 15 nov 2001
GRAumlTZEL M The light and shade of perovskite solar cells Nature Materials v 13 n 9 p 838ndash
842 2014
HADJIEV V G et al Phonon Fingerprints of CsPb2Br5 Single Crystals n Md p 1ndash5 maio
2018
HANUSCH F C et al Efficient Planar Heterojunction Perovskite Solar Cells Based on
Formamidinium Lead Bromide The Journal of Physical Chemistry Letters v 5 n 16 p 2791ndash
2795 ago 2014
HAO F et al Lead-free solid-state organic-inorganic halide perovskite solar cells Nature
Photonics v 8 n 6 p 489ndash494 2014
HERZBERG G Molecular Spectra and Molecular Structure II Infra-Red and Raman
Spectra of Polyatomic Molecules New Jersey - Princeton D Van Nostrand Company-Inc 1945
HUANG J et al Understanding the physical properties of hybrid perovskites for photovoltaic
applications Nature Reviews Materials v 2 2017
HUANG L et al Solar Energy Materials amp Solar Cells Multi-step slow annealing perovskite fi
lms for high performance pla- nar perovskite solar cells Solar Energy Materials and Solar Cells
v 141 p 377ndash382 2015
JAFFE A et al High-Pressure Single-Crystal Structures of 3D Lead-Halide Hybrid Perovskites
and Pressure Effects on their Electronic and Optical Properties ACS Central Science v 2 n 4
p 201ndash209 abr 2016
KIM M K JO V OK K M New Variant of Highly Symmetric Layered Perovskite with
Coordinated NO 3 minus Ligand Hydrothermal Synthesis Structure and Characterization of Cs 2 PbCl
2 (NO 3 ) 2 Inorganic Chemistry v 48 n 15 p 7368ndash7372 ago 2009
KOVALENKO M V PROTESESCU L BODNARCHUK M I Properties and potential
optoelectronic applications of lead halide perovskite nanocrystals Science v 358 p 745ndash750
2017
KRISHNAMURTHY S et al Molecular and Self-Trapped Excitonic Contributions to the
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
54
Broadband Luminescence in Diamine-Based Low-Dimensional Hybrid Perovskite Systems
Advanced Optical Materials v 1800751 p 1800751 26 jul 2018
LE Q VAN et al Low Temperature Solution-Processable Cesium Lead Bromide Microcrystals
for Light Conversion Crystal Growth amp Design p acscgd8b00264 2018
LEDINSKYacute M et al Raman Spectroscopy of OrganicndashInorganic Halide Perovskites The
Journal of Physical Chemistry Letters v 6 n 3 p 401ndash406 5 fev 2015
LI J et al Synthesis of all-inorganic CsPb2Br5perovskite and determination of its luminescence
mechanism RSC Advances v 7 n 85 p 54002ndash54007 2017a
LI M et al Colloidal CsPbX3(X = Br I Cl) NCs Morphology controlling composition evolution
and photoluminescence shift Journal of Luminescence v 190 n December 2016 p 397ndash402
2017b
LI P et al Novel synthesis and optical characterization of CsPb 2 Br 5 quantum dots in borosilicate
glasses Materials Letters v 209 p 483ndash485 dez 2017c
LI S et al Metal Halide Perovskite Single Crystals From Growth Process to Application
Crystals v 8 n 5 p 220 17 maio 2018
LIN H et al Low-Dimensional Organometal Halide Perovskites ACS Energy Letters v 3 n 1
p 54ndash62 2018
LIU Z et al Ligand Mediated Transformation of Cesium Lead Bromide Perovskite Nanocrystals
to Lead Depleted Cs4PbBr6Nanocrystals Journal of the American Chemical Society v 139 n
15 p 5309ndash5312 2017
LONG D A Introductory Raman Spectroscopy John R Ferraro Kazuo Nakamoto and Chris W
Brown Academic Press Amsterdam Second Edition 2003 xiii + 434 Journal of Raman
Spectroscopy v 36 n 10 p 1012ndash1012 out 2005
LONG J-Y YAN Z-S GONG Y Synthesis Structure and Band Gap of a Novel Inorganicndash
Organic Hybrid Material Based on Antimony Halide and Organoamine Crystallography
Reports v 63 n 3 p 433ndash437 2 maio 2018
LV J FANG L SHEN J Synthesis of highly luminescent CsPb2Br5nanoplatelets and their
application for light-emitting diodes Materials Letters v 211 p 199ndash202 2018
NAZARENKO O et al Luminescent and Photoconductive Layered Lead Halide Perovskite
Compounds Comprising Mixtures of Cesium and Guanidinium Cations Inorganic Chemistry v
56 n 19 p 11552ndash11564 2017
PHILIPPE B et al Chemical and Electronic Structure Characterization of Lead Halide Perovskites
and Stability Behavior under Different ExposuresmdashA Photoelectron Spectroscopy Investigation
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
55
Chemistry of Materials v 27 n 5 p 1720ndash1731 10 mar 2015
QIN C et al Centrifugal-Coated Quasi-Two-Dimensional Perovskite CsPb2Br5 Films for
Efficient and Stable Light-Emitting Diodes The Journal of Physical Chemistry Letters p
acsjpclett7b02371 2017
ROUSSEAU D L BAUMAN R P PORTO S P S Normal mode determination in crystals
Journal of Raman Spectroscopy v 10 n 1 p 253ndash290 jan 1981
RUAN L et al Alkyl-Thiol Ligand-Induced Shape- and Crystalline Phase-Controlled Synthesis
of Stable Perovskite-Related CsPb 2 Br 5 Nanocrystals at Room Temperature The Journal of
Physical Chemistry Letters v 8 n 16 p 3853ndash3860 ago 2017
SAIDAMINOV M I et al Pure Cs 4 PbBr 6 Highly Luminescent Zero-Dimensional Perovskite
Solids v 16 p 4 2018
SALIBA M et al Measuring Aging Stability of Perovskite Solar Cells Joule v 80 p 1ndash6 maio
2018
SARJEANT A A Structure Solution and Refinement with Olex2 A guide for Chem 435
Students [sl sn]
SETH S SAMANTA A Fluorescent Phase-Pure Zero-Dimensional Perovskite-Related
Cs4PbBr6Microdisks Synthesis and Single-Particle Imaging Study Journal of Physical
Chemistry Letters v 8 n 18 p 4461ndash4467 2017
SOE C M M et al New Type of 2D Perovskites with Alternating Cations in the Interlayer Space
(C(NH2)3)(CH3NH3)nPbnI3n+1 Structure Properties and Photovoltaic Performance Journal
of the American Chemical Society v 139 n 45 p 16297ndash16309 2017
STOUMPOS C C et al Crystal Growth of the Perovskite Semiconductor CsPbBr 3 A New
Material for High-Energy Radiation Detection Crystal Growth amp Design v 13 n 7 p 2722ndash
2727 2013a
SZAFRAŃSKI M KATRUSIAK A Mechanism of Pressure-Induced Phase Transitions
Amorphization and Absorption-Edge Shift in Photovoltaic Methylammonium Lead Iodide The
Journal of Physical Chemistry Letters v 7 n 17 p 3458ndash3466 set 2016
TANG X et al All-Inorganic Perovskite CsPb2Br5 Microsheets for Photodetector Application
Frontiers in Physics v 5 n January p 1ndash7 2018
TILLEY J D R Perovskites First Edit ed United Kingdom Wiley 2016
TOBERGTE D R CURTIS S Crystals and crystal structures [sl sn] v 53
TSAI H et al High-efficiency two-dimensional ruddlesden-popper perovskite solar cells Nature
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
56
v 536 n 7616 p 312ndash317 2016
TSAI H et al Design principles for electronic charge transport in solution-processed vertically
stacked 2D perovskite quantum wells Nature Communications p 1ndash9 2018
VOLOSHINOVSKII A MYAGKOTA S LEVITSKII R Luminescence of Ferroelastic
CsPbCl 3 Nanocrystals Ferroelectrics v 317 n 1 p 119ndash123 2005
WANG K-H et al Large-Scale Synthesis of Highly Luminescent Perovskite-Related CsPb 2 Br
5 Nanoplatelets and Their Fast Anion Exchange Angewandte Chemie International Edition v
55 n 29 p 8328ndash8332 jul 2016a
WANG L et al Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal
Halide Perovskite-Based Methylammonium Lead Chloride The Journal of Physical Chemistry
Letters v 7 n 24 p 5273ndash5279 15 dez 2016b
WANG L WANG K ZOU B Pressure-Induced Structural and Optical Properties of
Organometal Halide Perovskite-Based Formamidinium Lead Bromide Journal of Physical
Chemistry Letters v 7 n 13 p 2556ndash2562 2016
WANG P et al Solvent-controlled growth of inorganic perovskite films in dry environment for
efficient and stable solar cells Nature Communications v 9 n 1 p 2225 8 dez 2018a
WANG Y et al Pressure-Induced Phase Transformation Reversible Amorphization and
Anomalous Visible Light Response in Organolead Bromide Perovskite Journal of the American
Chemical Society v 137 n 34 p 11144ndash11149 2015
WANG Y et al Solution-Grown CsPbBr 3 Cs 4 PbBr 6 Perovskite Nanocomposites Toward
Temperature-Insensitive Optical Gain Small v 13 n 34 p 1701587 set 2017
WANG Y et al Bright Luminescent Surface States on the Edges of Wide-bandgap Two-
dimensional Lead Halide Perovskite p 1ndash16 mar 2018b
XIE L-Q et al Organicndashinorganic interactions of single crystalline organolead halide perovskites
studied by Raman spectroscopy Phys Chem Chem Phys v 18 n 27 p 18112ndash18118 2016
YANG R X et al Spontaneous octahedral tilting in the cubic inorganic cesium halide perovskites
CsSnX3and CsPbX3(X = F Cl Br I) Journal of Physical Chemistry Letters v 8 n 19 p
4720ndash4726 2017
YIN J et al Supporting Information Intrinsic Lead Ion Emissions in Zero-dimensional Cs 4 PbBr
6 Nanocrystals [sd]
YIN J et al Molecular behavior of zero-dimensional perovskites Science Advances v 3 n 12
p e1701793 2017a
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d
57
YIN J et al Intrinsic Lead Ion Emissions in Zero-Dimensional Cs4PbBr6 Nanocrystals ACS
Energy Letters v 2 n 12 p 2805ndash2811 2017b
ZEWEN XIAO C et al Materials Horizons rsclimaterials-horizons Searching for promising new
perovskite-based photovoltaic absorbers the importance of electronic dimensionality Searching
for promising new perovskite-based photovoltaic absorbers the importance of electronic v 4 p
206 2017
ZHANG B BIN et al The preparation and characterization of quasi-one-dimensional lead based
perovskite CsPbI3crystals from HI aqueous solutions Journal of Crystal Growth v 498 n May
p 1ndash4 2018a
ZHANG H et al Pure zero-dimensional Cs4PbBr6 single crystal rhombohedral microdisks with
high luminescence and stability Physical Chemistry Chemical Physics v 19 n 43 p 29092ndash
29098 2017
ZHANG L et al Pressure-Induced Structural Evolution and Optical Properties of Metal Halide
Perovskite CsPbCl3 The Journal of Physical Chemistry C p acsjpcc8b05397 15 jun 2018b
ZHANG L ZENG Q WANG K Pressure-Induced Structural and Optical Properties of
Inorganic Halide Perovskite CsPbBr3 Journal of Physical Chemistry Letters v 8 n 16 p
3752ndash3758 2017a
ZHANG Q YIN Y All-Inorganic Metal Halide Perovskite Nanocrystals Opportunities and
Challenges 2018
ZHANG Z et al Growth characterization and optoelectronic applications of pure-phase large-
area CsPb2 Br5 flake single crystals Journal of Materials Chemistry C v 6 n 3 p 446ndash451
2018d